key

serving as an essential component

“a cardinal rule”

metal device shaped in such a way that when it is inserted into the appropriate lock the lock's mechanism can be rotated

a lever (as in a keyboard) that actuates a mechanism when depressed

the central building block at the top of an arch or vault

mechanical device used to wind another device that is driven by a spring (as a clock)

pitch of the voice

“he spoke in a low key”

something crucial for explaining

“the key to development is economic integration”

a generic term for any device whose possession entitles the holder to a means of access

“a safe-deposit box usually requires two keys to open it”

a list of words or phrases that explain symbols or abbreviations

a list of answers to a test

“some students had stolen the key to the final exam”

any of 24 major or minor diatonic scales that provide the tonal framework for a piece of music

(basketball) a space (including the foul line) in front of the basket at each end of a basketball court; usually painted a different color from the rest of the court

“he hit a jump shot from the top of the key”

a coral reef off the southern coast of Florida

a winged often one-seed indehiscent fruit as of the ash or elm or maple

a kilogram of a narcotic drug

“they were carrying two keys of heroin”

harmonize with or adjust to

“key one's actions to the voters' prevailing attitude”

regulate the musical pitch of

identify as in botany or biology, for example

vandalize a car by scratching the sides with a key

“His new Mercedes was keyed last night in the parking lot”

provide with a key

“We were keyed after the locks were changed in the building”