key

Dictionary definition · 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)
metal device shaped in such a way that when it is inserted into the appropriate lock the lock's mechanism can be rotated
something crucial for explaining"the key to development is economic integration"
pitch of the voice"he spoke in a low key"
any of 24 major or minor diatonic scales that provide the tonal framework for a piece of music
a kilogram of a narcotic drug"they were carrying two keys of heroin"

identify as in botany or biology, for example
provide with a key"We were keyed after the locks were changed in the building"
vandalize a car by scratching the sides with a key"His new Mercedes was keyed last night in the parking lot"
regulate the musical pitch of
harmonize with or adjust to"key one's actions to the voters' prevailing attitude"

Source: Open English WordNet (CC BY 4.0).