Sailor joins party workers in the middle? (7)
I believe the answer is:
Here is my best explanation:
'the middle?' is the definition.
'sailor joins party workers' is the wordplay.
'sailor' becomes 'ab' (abbreviation for able seaman).
'joins' says to put letters next to each other.
'party' becomes 'do' (do is a kind of party).
'workers' becomes 'men' (man is a kind of worker).
'in' acts as a link.
(Other definitions for abdomen that I've seen before include "Site of corporation", "Midriff", "pot", "Part of body containing the stomach", "Belly", "corporation's site", "Central part of the body", "Where one digests", "Stomach" and "Region of the body between the thorax and pelvis".)