Crossword Genius

An old joke (4)

Ross

I believe the answer is:

jest

I'm a little stuck... Click here to teach me more about this clue!

This clue could be a double definition.

'an old' is the first definition.
Although both the answer and definition are singular nouns, I cannot understand how one could define the other.

'joke' is the second definition.
(I know that joke can be written as jest)

Can you help me to learn more?

(Other definitions for jest that I've seen before include "Quip" , "Humorous remark" , "it's not serious, so to speak" , "Scoff; playfulness" , "Sally" .)

I've seen this clue in The Globe and Mail.
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