Song about a sailor in Asia (6)
I believe the answer is:
arabia
'in asia' is the definition.
('Arabia' is part of 'asia')
'song about a sailor' is the wordplay.
'song' becomes 'aria' (aria is a kind of song).
'about' is an insertion indicator.
'a sailor' becomes 'ab' (abbreviation for able seaman).
'aria' enclosing 'ab' is 'ARABIA'.
(Other definitions for arabia that I've seen before include "World's largest peninsula" , "Peninsula of SW Asia" , "Asian peninsular" , "Region between the Red Sea and Persian Gulf" , "TE Lawrence's milieu?" .)