A smooth, reddish-brown nut that grows inside a spiky shell, or a horse with a reddish-brown coat; also a tired, old joke.
From Old French 'chastaigne,' from Latin 'castanea,' which came from Greek 'kastanon,' possibly borrowed from Asia Minor. The tree was named by Mediterranean civilizations that encountered it.
A 'chestnut' as a joke refers to an 1816 English play where a character tells the same joke repeatedly—making it the original 'it's an oldie but goldie,' and linguistically freezing that specific form of tedium into a single word.
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