Part of body of soldiers joining sailor before party (7)
I believe the answer is:
abdomen
'part of body' is the definition.
('abdomen' is part of 'body')
'soldiers joining sailor before party' is the wordplay.
'soldiers' becomes 'men' (I've seen this before**).
'joining' is a charade indicator (letters next to each other).
'sailor' becomes 'ab' (abbreviation for able seaman).
'before' means one lot of letters go next to another.
'party' becomes 'do' (do is a kind of party).
'ab'+'do'='abdo'
'men' after 'abdo' is 'ABDOMEN'.
'of' is the link.
(Other definitions for abdomen that I've seen before include "4 part of insect" , "Central part of the body" , "Where one digests" , "Tummy" , "Ban demo (anag)" .)