Niminy-piminy (4)
I believe the answer is:
prim
'niminy-piminy' is the definition.
(synonyms)
This is the entire clue.
(Other definitions for prim that I've seen before include "Schoolmarmish" , "Proper or prissy" , "Proper (type of rose?)" , "Straight-laced" , "Stiffly formal and proper" .)