Profit about right for corn (5)
I believe the answer is:
grain
'for corn' is the definition.
(I've seen this before)
'profit about right' is the wordplay.
'profit' becomes 'gain' (synonyms).
'about' means one lot of letters goes inside another.
'right' becomes 'r' (common abbreviation).
'gain' going around 'r' is 'GRAIN'.
(Other definitions for grain that I've seen before include "Cereal crops" , "Small piece of sand" , "Small particle - wood texture" , "Small quantity (of corn etc)" , "basis for whisky" .)