Lengthen a sentence? (7)

I believe the answer is:

stretch

This clue is a double definition.

'lengthen' is the first definition.
(I know that stretch is a kind of lengthen)

'a sentence' is the second definition.
(a stretch in prison)

(Other definitions for stretch that I've seen before include "Straighten the arms" , "sort of limousine" , "extension" , "Strain" , "Extend, time spent in prison" .)

I've seen this clue in The Irish Independent and the Evening Standard.

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