It's perfectly natural to play instrument with nice interns (7)
I believe the answer is:
organic
'it's perfectly natural to play' is the definition.
I can't tell whether this definition defines the answer.
'instrument with nice interns' is the wordplay.
'instrument' becomes 'organ' (organ is a kind of instrument).
'with nice interns' becomes 'ic' (I am not sure about this - if you are sure you should believe this answer much more).
'organ'+'ic'='ORGANIC'
Can you help me to learn more?
(Other definitions for organic that I've seen before include "structured" , "Relating to living matter" , "Pesticide-free" , "(Compound) containing carbon" , "Got from living matter" .)