| 1. | Machinery. a groove in a shaft, the hub of a wheel, etc., for receiving part of a key holding it to another part. |
| 2. | a slot in a lock for receiving and guiding the key. |
| 3. | (in poured-concrete construction) a longitudinal groove in a footing, or in a pour that has set, providing a key for newly poured concrete. |
| 4. | a depression or slot carved into rock to provide a bond or anchorage for a structure, as a dam. |