Overly proper person (5)
I believe the answer is:
prude
'overly proper person' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for prude that I've seen before include "Type overly concerned with decorum" , "One easily shocked by impropriety" , "Puritan, prig" , "old maid" , "One is excessively concerned with propriety and decorum" .)