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 subsidiary indication.
'sailor' becomes 'ab' (abbreviation for Able Bodied).
'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' is the link.
(Other definitions for abdomen that I've seen before include "The belly", "Mean bod (anag.)", "Central part of the body", "Midriff", "The body between chest and diaphragm", "Bodily region", "Region of the body between the thorax and pelvis", "Stomach", "4 part of insect" and "Part of the body below chest and diaphragm".)