Sailor rejecting seafood, being sole (5)
I believe the answer is:
alone
'being sole' is the definition.
('alone' can be a synonym of 'sole')
'sailor rejecting seafood' is the wordplay.
'sailor' becomes 'ab' (abbreviation for able seaman).
'rejecting' is a deletion indicator.
'seafood' becomes 'abalone' (type of sea snail).
'abalone' with 'ab' taken out is 'ALONE'.
(Other definitions for alone that I've seen before include "Solo" , "Singly" , "Unaccompanied" , "Without others being involved" , "Without others present" .)