Meaning

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

noun something crucial for explaining

noun pitch of the voice

originFrom Middle English keye, kaye, keiȝe, from Old English cǣġ (“key, solution, experiment”) (whence also Scots key and kay (“key”)), from Anglo-Frisian Proto-West Germanic *kaiju, of uncertain origin. The only sure cognates are Saterland Frisian Koai (“key”), West Frisian kaai (“key”), and North Frisian kai, koie (“key”). Possibly from Proto-Germanic *kēgaz, *kēguz (“stake, post, pole”), from…

Etymology from Wiktionary, CC BY-SA 3.0