keyway

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A slot for a key in the hub or shaft of a wheel.
• noun The keyhole of a cylinder lock.

from The Century Dictionary.

• noun A mortise made for the reception of a key; a slot in the round hole of a wheel for the reception of the key whereby the wheel is secured to the shaft.

from the GNU version of the Collaborative International Dictionary of English.

• noun See Key way, under key.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A slot into which a precision attachment (a key) is fitted