Greek character with skittle to contribute (4,2)
I believe the answer is:
chip in
'to contribute' is the definition.
(synonyms)
'greek character with skittle' is the wordplay.
'greek character' becomes 'chi' (letter from the Greek alphabet).
'with' means one lot of letters go next to another.
'skittle' becomes 'pin' (I've seen this before).
'chi'+'pin'='CHIP-IN'
(Other definitions for chip in that I've seen before include "Make a contribution" , "hole the ball" , "Interpose" , "add to the kitty" , "Pay part of the cost of something" .)