No secret tune outside (7)
I believe the answer is:
openair
'no secret' is the definition.
I don't know anything about this answer so I can't judge whether it can be defined by this definition.
'tune outside' is the wordplay.
I cannot really see how this works, but
'tune' could be 'air' (air can mean a piece of music) and 'air' is found in the answer.
'outside' could be 'open' (open is a kind of outside) and 'open' is located in the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for openair that I've seen before include "taking place out of doors" , "Outdoor" .)