Fellow bachelor carrying less weight (8)
I believe the answer is:
blighter
'fellow' is the definition.
(I know that fellow can be written as blighter)
'bachelor carrying less weight' is the wordplay.
'bachelor' becomes 'B' (abbreviation e.g. BA=Bachelor of Arts).
'carrying less weight' becomes 'lighter' (lighter means less heavy).
'b'+'lighter'='BLIGHTER'
(Other definitions for blighter that I've seen before include "Beggar" , "irritating person" , "Villain" , "so-and-so" , "Cad" .)