Seafood for sailor, unaccompanied (7)
I believe the answer is:
abalone
'seafood' is the definition.
(type of sea snail)
'sailor unaccompanied' is the wordplay.
'sailor' becomes 'ab' (abbreviation for able seaman).
'unaccompanied' becomes 'alone' (synonyms).
'ab'+'alone'='ABALONE'
'for' acts as a link.
(Other definitions for abalone that I've seen before include "Source of mother-of-pearl" , "Mollusc also called ormer" , "shellfish for instance" , "Would you be able on a US shellfish?" , "Ormer, ear shell" .)