Fun for a singer on the ascendancy (4)
I believe the answer is:
'fun' is the definition.
(I've seen this before)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for lark that I've seen before include "Flighty type" , "what one may get up to?" , "in-flight performer" , "Mess about" , "Songbird - 3" .)