Belly dancer initially covered by sailor on sign (7)
I believe the answer is:
abdomen
'belly' is the definition.
('abdomen' can be a synonym of 'belly')
'dancer initially covered by sailor on sign' is the wordplay.
'initially' says to take the initial letters.
'covered by' says to put letters next to each other (on top of in a down clue).
'sailor' becomes 'ab' (abbreviation for able seaman).
'on' means one lot of letters go next to another.
'sign' becomes 'omen' (omen is a kind of sign**).
The first letter of 'dancer' is 'd'.
'd' after 'ab' is 'abd'.
'abd'+'omen'='ABDOMEN'
(Other definitions for abdomen that I've seen before include "corporation's site" , "Central part of the body" , "Bodily region" , "Part of the body below chest and diaphragm" , "A main part of the body" .)