key

A shaped piece of metal inserted into a lock and turned to open or close it.

• He reached into his pocket and realized he had left the front door key inside.

A crucial element, factor, or solution that provides access or understanding.

• Clear communication among team members proved to be the key to completing the project on time.

One of several buttons or levers pressed on a keyboard, typewriter, or musical instrument.

• She pressed the enter key to submit her application before the deadline passed.