Keywords are a new feature in version 3.6. Keywords are a single word, or a short phrase that is shared across multiple cards. Regardless of what card the Keyword is on, it will always act the same. Keywords allow cards to discribe complicated systems in very little text. Below you can find a list of keywords with example cards, organized by card difficuly.

Before getting into Keywords, it is important to understand the basics of what cards do.

+1 Card simply means to draw 1 card from your deck.
+1 Action means that you have 1 more Action point this turn. You need to have at least 1 Action point to play an Action card.
+1 Buy means that you have 1 more Buy point this turn. Any time that you want to buy a card you must have at least 1 Buy point to do so.
+1 Coin means that you have $1 more to spend this turn to buy something.

Some cards will ask you to discard cards. These cards are asking you to select cards from your hand that you want to discard. Some cards like Celler allow you to discard as many cards as you want, while other cards may tell you discard a specific number of cards. If you ever cannot discard the number of cards asked, you must discard as many as you have.
Cards that you discard are placed into your discard pile. If you ever try to draw a card, but your deck is empty, your discard pile is shuffled and becomes your new deck.

Some cards will ask you to gain a card meeting certain conditions. Sometimes these cards are asking you to choose a card to gain from the Supply, while other times they are talling you to gain a specific card from the Supply.
The gained card is then placed into your discard (unless otherwise stated).

Some cards will ask you to trash a card. These cards are asking you to select a card from your hand (or they might just trash themselves).
The selected card is then placed into a communal pile of trashed cards. These cards no longer belong to you or anybody. You will never see the trashed card in your deck again, it is permanently gone.

The Complete Deck keyword refers to all cards that a player owns, regardless of where they are. This includes any cards that the player has set aside during the game. The only cards not included are cards that the player has Trashed.

The On Buy: keyword is triggered when you buy a card. This effect is different from On Gain: in that it will only tirgger if you buy the card during your Buy phase.

The On Gain: keyword is triggered when you gain a card through any means. Buying the card will trigger the On Gain: effect.

The Search keyword is used on cards that look through your deck for one or more cards. Search starts with the top of your deck and works down through it. If Search does not find what it is looking for in your deck, it will then look through your Discard. Unless stated otherwise, cards that do not match the search criteria will be discarded.

The Buy Phase: keyword refers to the phase of your turn when you start to buy cards. This phase occures after you have played your treasure, or as soon as you attempt to buy a card that you can afford. Some cards like those listed above have a different cost during the Buy Phase.

The Cleanup: keyword triggers at the very end of your turn. Cards with the Cleanup: keyword have an ability that triggers during the Cleanup phase if that card is in play. If the card is not in play, nothing happens. There are 2 exceptions to this rule, both Province, and Colony use the Cleanup: keyword regardless of where the Province or Colony is.

The Duration: keyword can only be found on Duration cards. This keyword translates to: "At the start of your next turn, if this card is in play:". Duration cards, unless stated otherwise, stay in play for an additional turn before they are discarded from play. Note: while you can use cards like Throne Room on a Duration card, its Duration: effect will only trigger once per copy of the card in play.

The On Trash: keyword triggers when that specific card is trashed. On Trash: will only trigger if a player owned the card before it was trashed, so you cannot trigger On Trash: with cards such as Strip Mine.

Overpay: is a special system that allows players to pay extra when Buying a card. It can only be triggered once when the card is bought, and cannot be trigged when the card is Gained. Generally when you Overpay: for a card you will get a bonus for every 1 Coin overpaid.

The Reaction: keyword is a very general keyword that is simply used any time a card reacts to an event in the game. Each Reaction card will tell you what its specific Reaction: does. Note that Reaction cards trigger automatically, as long as the Reaction card is in your hand.

The Setup: keyword is only found on a few cards, and it is triggered exactly once at the very start of each game. The Setup: effect triggers before the first player takes their first turn.

Special Cards are cards which cannot be bought at all, and can only be gained if another specific card tells you to gain a Special Card. Some Special Cards such as Shelters and the Overgrown cards will sometimes replace a player's starting 3 estates.

The Attack keyword is used by Attack cards. Attacks negativly affect other players. An Attack can be Reacted to with the Defense keyword.

The Defense keyword is used by Reaction cards. Defense triggers when the player who has the Reaction card in their hand is Attacked. This type of reaction is automatic will always happen if the Reaction card is in the attacked player's hand.

This Discover keyword is nearly a direct copy from Heathstone. What this keyword means is: "Choose 1 of the following 3 cards. These 3 cards were chosen randomly from outside of the Suppply." Each card that uses the Discover keyword will tell you what the restrictions are on the cards that you can choose from.

The Grandeur keyword is used on a few specific cards. This keyword means that when bought, an additional cost can be paid to modify the text of the bought copy of the card. A card whos Grandeur is paid, is then upgraded to a better version of itself, with different text.

The Growth keyword is a card specific token system. Unlike other tokens, each card that uses Growth is independent of every other card, even cards with the same name. Unless otherwise states, Growth cards will grow each time they are played.

The Max Growth keyword is used to balance several Growth cards. Max Growth prevents several specific cards from growing infinitly.

The On Draw keyword triggers when the specific card that it is on, is drawn from the player's deck. Regardless of anything else (such as what phase of the turn it is, or even if the owner of the drawn card is the current player), On Draw will always trigger.

The Permanent Duration keyword is used only on the above cards. Duration cards with this keyword never leave play once played (unless another card forces them to). This means that this cards only need to be played once, and then their effect will happen at the start of each turn for the rest of the game.

The Permanent Effect keyword is similar to the Permanent Duration keyword, in that is it only found on a few specific Duration cards. Unlike the Permanent Duration keyword, the Permanent Effect keyword triggers at a specific time (stated on each card) and not at the start of each turn.

The While This Is In Play keyword does exactly what it says. While a card that uses the While This Is In Play keyword is in play, the stated effect takes place. There are a few ways to play a card that do not involve simply putting the card into play, in which case this keyword would not trigger. For example, you could use the card Procession to play one of the above cards twice, and then trash the card. While the card would enter play, it would then be trashed, thus leaving play. In addition, a card like Throne Room that simply plays the card twice, will not trigger While This Is In Play more than once, as even though the card was played twice, it is only in play once.

The Guild Card keyword is only used on a few cards which, when found in game, are all part of the same pile of cards. If this pile is in a game, you will see only the top card of this pile. The pile is made up of a random assortment of Guild cards in a random order. Only the top card of the pile can ever be seen or gained.

The Event keyword is only used on Event cards. Event cards cannot be gained by any means. During your buy phase you can pay their cost and 1 buy to trigger them. When triggered, you do whatever the card says immedietly. Event cards are part of the Supply but there is only ever one copy of an Event card and it can never leave the Supply.

Ancient Effect is one of several keywords only used by Ancient Ones. This keyword translates to: if you control this card, regardless of where it is, do something specific at a specific time. It can vary from giving you a bonus at the start of each of your turns, to having an affect after you play a type of card.

The Ancient One keyword is used to convey multiple peices of information.
First, you can only gain 1 copy of a card with this name. This is important because when found in games, Ancient ones appear with a single copy of an Ancient One, and 1 copy per player of a Favor of that Ancient One.
Second, if the pile that the Ancient One is in is empty, it does not count towards the total number of piles that are empty. This matters for some specific cards that check how many piles are empty (City, Smokestack) or to see if enough piles are empty for the game to end.
Third, when you gain an Ancient One it is automatically set aside for you. Ancient Ones do not take up any space in your deck, and you can never draw them. Only using very specific cards can you override this and place an Ancient One into your deck.
Finally, while an Ancient One can be placed into the trash pile, once it has been gained, its owner never changes. This means that even if you manage to find a way to trash an Ancient One (or pass it with a Masquerade), whoever first gained the Ancient One will always keep its benifit.

The Modified Cost keyword is found on several Ancient Ones and it means that the cost of the card is determined at the start of the game based on if the there are Colonies and or Potions in the game. Sometimes, Ancient Ones will cost a Potion (if there are Potion cards), or cost more coins (if there are Colonies).

Azathoth stands alone as the only Ancient One with a Passive Effect. This keyword means that Azathoth will affect every player regardless of where Azathoth is, even if it is in the Supply.

Potion Card refers to any card which either costs at least 1P, or can produce at least 1P, or directly interacts with a card that costs at least 1P.

Starting Deck refers to the 10 cards that each player starts the game with. Usually this means your starting 7 Coppers and 3 Estates, but sometimes these cards are replaced by other cards before the game starts.

Untrashable is only used by Dimensional Portal, and is only used so that there is as much space as possible on the card to display cards that it sets aside. Untrashable does what it sounds like, in that it makes Dimensional Portal incapable of being trashed. While you can select Dimenional Portal to trash it, it will immediately return to wherever it was before it was trashed.