Proportion kept by corporation (5)
I believe the answer is:
ratio
'proportion' is the definition.
(thesaurus)
'kept by corporation' is the wordplay.
'kept by' indicates the answer is hidden within the clue.
'RATIO' is hidden in the letters of 'corporation'.
(Other definitions for ratio that I've seen before include "A trio (anag)" , "One-to-one, maybe" , "E.g. two to one" , "Relationship found in a riot" , "Relationship between two amounts" .)