General:
* Keyhole
* Keychain
* Keycard
* Keynote (also a noun, meaning the central theme)
* Keystroke
* Keypad
* Keyman
* Keystone (meaning the central or essential part)
* Keyring
More specific:
* Keymaster (a person responsible for keys)
* Keyhole surgery (a minimally invasive surgical technique)
* Key press (the act of pressing a key on a keyboard)
* Key signature (the musical notation indicating the key of a piece)
* Key ingredient (the most important ingredient in a recipe)
* Key player (a crucial member of a team or group)
Let me know if you would like me to generate more examples or compound words related to a specific theme!