By Robin, is it modern music? (5)
I believe the answer is:
adair
'by robin' is the definition.
'adair' can be an answer for 'robin' (I've seen this in another clue). I am not certain of the 'by' bit.
'it modern music?' is the wordplay.
I cannot really see how this works, but
'modern' could be 'ad' (I've seen this in other clues) and 'ad' is present in the answer.
'music?' could be 'air' (air is a kind of music) and 'air' is located in the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
'is' acts as a link.
Can you help me to learn more?
(Another definition for adair that I've seen is " Robin - - (old song)".)