Lengthen a sentence (7)

I believe the answer is:

stretch

I believe this is a double definition.

'lengthen' is the first definition.
(I know that stretch is a more specific form 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 Evening Standard and The Irish Independent.

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