key

1. key (noun) — sense 1

Definition: An object designed to open and close a lock or to activate or deactivate something, especially a length of metal inserted into a narrow opening on the lock to which it is matched (keyed).

Example: This key is to the backdoor.

2. key (noun) — sense 2

Definition: An object designed to open and close a lock or to activate or deactivate something, especially a length of metal inserted into a narrow opening on the lock to which it is matched (keyed).: A card or fob that electronically signals a lock to open.

Example: My hotel room key is a card.

3. key (noun) — sense 3

Definition: An object designed to open and close a lock or to activate or deactivate something, especially a length of metal inserted into a narrow opening on the lock to which it is matched (keyed).: A piece of information (e.g., a password or passphrase) used to encode or decode a message or messages.

4. key (adj) — sense 4

Definition: Indispensable, supremely important.

Example: He is the key player on his soccer team.

5. key (adj) — sense 5

Definition: Important, salient.

Example: She makes several key points.

6. key (verb) — sense 6

Definition: To fit (a lock) with a key.

7. key (verb) — sense 7

Definition: To fit (pieces of a mechanical assembly) with a key to maintain the orientation between them.

8. key (verb) — sense 8

Definition: To mark or indicate with a symbol indicating membership in a class.

Example: So I worked on a tissue-paper copy of the perimeter plan, outlining groupings of plants of the same species and keying them with letters for the species.