Shoot in season, having no end of fun (5)
I believe the answer is:
sprig
'shoot' is the definition.
(I've seen this before)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for sprig that I've seen before include "Headless nail; leafy ornament" , "Young shoot" , "piece of holly" , "Small leafy stem" , "Tiny branch" .)