I believe the answer is:
'exasperated' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for fed up that I've seen before include "Hacked off" , "far from happy?" , "Informally bored or discontented (3,2)" , "as pigs are to be slaughtered?" , "Bored - disgusted" .)