A bit in favour of weight (6)
I believe the answer is:
proton
'a bit' is the definition.
The answer and definition can be both natural objects as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'in favour of weight' is the wordplay.
'in favour of' becomes 'pro' (being pro a particular cause).
'weight' becomes 'ton' (unit of weight).
'pro'+'ton'='PROTON'
Can you help me to learn more?
(Other definitions for proton that I've seen before include "just a little bit" , "Particle in atoms" , "One charged" , "Positive thing" , "Positive nucleon" .)