Small ape overall (5)
I believe the answer is:
smock
'overall' is the definition.
'small ape' is the wordplay.
I cannot quite understand how this works, but
'small' could be 'sm' and 'sm' is present in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for smock that I've seen before include "artist's attire" , "Loose outer garment" , "Artist's loose overall" , "Loose dress or blouse" , "Loose overall or dress" .)