Notes OAP is terrible stirrer (8)
I believe the answer is:
teaspoon
'stirrer' is the definition.
(I've seen this before)
'notes oap is terrible' is the wordplay.
'is terrible' is an anagram indicator.
'notes'+'oap'='notesoap'
'notesoap' with letters rearranged gives 'TEASPOON'.
(Other definitions for teaspoon that I've seen before include "Five millilitres (cookery)" , "It creates a stir" , "Small medicine dispensing unit" , "Small stirrer" , "Cooking unit" .)