Fit for serving (10)
I believe the answer is:
proportion
'fit' is the definition.
(thesaurus)
'for serving' is the wordplay.
'for' becomes 'pro' (I've seen this before).
'serving' becomes 'portion' ('portion' can be a synonym of 'serving').
'pro'+'portion'='PROPORTION'
(Other definitions for proportion that I've seen before include "balance" , "Part - one needs a sense of it" .)