Committee fed up, one might say (5)
I believe the answer is:
board
'committee' is the definition.
(board is a kind of committee)
'fed up one might say' is the wordplay.
'fed up' becomes 'bored' (fed up can mean bored).
'one might say' shows a homophone (sound like).
'bored' sounds like 'BOARD'.
(Other definitions for board that I've seen before include "Supervisory committee" , "Food - table - directors" , "Decision-making body" , "See 21 Down" , "See 9" .)