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

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

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

key (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

key a coral reef off the southern coast of Florida

key United States lawyer and poet who wrote a poem after witnessing the British attack on Baltimore during the War of 1812; the poem was later set to music and entitled `The Star-Spangled Banner'' (1779-1843)

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

key identify as in botany or biology, for example

key serving as an essential component

key effective; producing a desired effect