keyway

noun

1. A slot into which a precision attachment (a key) is fitted.
2. The whole deep way the key has to go, the hollow or cavity.
3. A guide groove.
4. The recessed part of a keyed joint, in which the key resides.

   “Near-synonyms: keyseat, groove”

5. The groove within a modern lock that the key slides into; any lock's keyhole.