Monkey makes gaffe (6)
I believe the answer is:
howler
This clue is a double definition.
'monkey' is the first definition.
(I know that howler is a type of New World monkey)
'gaffe' is the second definition.
(I've seen this before)
'makes' acts as a link.
(Other definitions for howler that I've seen before include "Gaffe" , "Schoolboy error - wolf?" , "Glaring error" , "Grievous error" , "Glaring mistake made by schoolboy" .)