Finish work and hit the hay (6)

I believe the answer is:

retire

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'hit the hay' is the definition.
(synonyms)

I cannot understand how the rest of the clue works.

(Other definitions for retire that I've seen before include "go upstairs?" , "Give up work for good" , "Finish following one's career" , "climb the stairs" , "Give up working and go to bed" .)

I've seen this clue in The Sun.

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