Homer's grunt (3)
I believe the answer is:
doh
'homer's grunt' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for doh that I've seen before include "Stupid me!" , "an exclamation from someone who's annoyed with himself" , "The note C" , "annoyed expression" , "Homeric grunt of annoyance" .)