backed out of something because of fear or lack of courage; chickened out means to lose your nerve at the last moment.
From 'chicken,' Old English 'cicen' or 'chicken,' a young fowl. Became slang as a taunt for cowardice around 1600s, possibly because chickens are easily frightened. 'Chickened out' became standard by the 1900s.
Calling someone a 'chicken' for being scared is ancient English trash talk, but it reveals something strange—we assign moral judgment to animal characteristics, as if showing self-preservation (what chickens do) is actually a character flaw.
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