In which someone takes his time (4)

I believe the answer is:

cell

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'in which someone takes his time' is the definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.

This is the entire clue.

Can you help me to learn more?

(Other definitions for cell that I've seen before include "Monk's small room" , "Biological unit with a nucleus" , "Part of a battery" , "American mobile" , "Place for a prisoner" .)

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

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