A berry good lark! (5)
I believe the answer is:
caper
'lark' is the definition.
(I've seen this before)
'a berry good' is the wordplay.
I cannot really see how this works, but
'a' could be 'per' (eg 'one a day' means 'one per day') and 'per' is present in the answer.
The remaining letters 'ca' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for caper that I've seen before include "Skip about for the sauce" , "Recap about prank" , "Dance playfully" , "Pickle ingredient" , "Cooked and pickled flower bud" .)