Stomach muscle to work at, chaps (7)
I believe the answer is:
abdomen
'stomach' is the definition.
('abdomen' can be a synonym of 'stomach')
'muscle to work at chaps' is the wordplay.
'muscle' becomes 'ab' (short for abdominal muscle).
'to work' becomes 'do' ('do work' can be a synonym of 'work'**).
'at' says to put letters next to each other.
'chaps' becomes 'men' (I've seen this before).
'ab'+'do'+'men'='ABDOMEN'
(Other definitions for abdomen that I've seen before include "gut" , "Part of body containing the digestive organs" , "Where one digests" , "pot" , "Site of corporation" .)