key
UK: kiː | US: kiː
n. 1. A small metal instrument used to operate a lock.
n. 2. A crucial or central element for understanding or achieving something.
n. 3. A button or lever on a keyboard or musical instrument.
adj. 4. Of primary importance; essential.
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The word "key" traces back to Old English cǣg, which referred specifically to a metal tool for locking or unlocking. Its Germanic roots (compare Old Frisian kei, Middle Dutch caye) suggest an ancient focus on the physical object. Over time, "key" expanded metaphorically to denote centrality or importance (e.g., "key to success"), reflecting how physical keys grant access—just as abstract "keys" unlock solutions. The spelling remained stable, though pronunciation shifted from Old English /kæːɡ/ to modern /kiː/.
She turned the key and opened the door.
Hard work is the key to mastering a skill.
Press the "Enter" key to confirm your selection.
Trust is a key component in any relationship.
The pianist struck the wrong key during the performance.