key

A low offshore island or reef, especially in the Gulf of Mexico; a cay.

A kilogram of marijuana, cocaine, or heroin.

A notched and grooved, usually metal implement that is turned to open or close a lock.

A similar implement or an electronic device used for opening, winding, or starting something.

A device, such as a wedge or pin, inserted to lock together mechanical or structural parts.

A keycard.

A determining factor in accomplishing or achieving something.

Something that provides access to or understanding of something else.