Gentle entertainment at river, lying around eating tree nuts (8)
I believe the answer is:
operetta
'gentle entertainment' is the definition.
'operetta' can be an answer for 'entertainment' (I've seen this before). I'm not sure about the 'gentle' bit.
'at river lying around eating tree nuts' is the wordplay.
'river' becomes 'po' (Italian river).
'lying around' says the letters should be written in reverse.
'eating' means one lot of letters goes inside another.
'nuts' is an anagram indicator (nuts can mean crazy).
'at'+'po'='atpo'
'atpo' in reverse letter order is 'opta'.
'tree' with letters rearranged gives 'eret'.
'opta' going around 'eret' is 'OPERETTA'.
Can you help me to learn more?
(Other definitions for operetta that I've seen before include "The Mikado or The Gondoliers, say" , "Show" , "light-hearted performance" , "Musical entertainment" , "Theatre piece" .)