Frisky horse up for mythical musician (7)
I believe the answer is:
orpheus
'mythical musician' is the definition.
(I've seen this before)
'frisky horse up' is the wordplay.
'frisky' is an anagram indicator.
'horse'+'up'='horseup'
'horseup' anagrammed gives 'ORPHEUS'.
'for' acts as a link.
(Other definitions for orpheus that I've seen before include "Husband to Eurydice" , "musician inspiring many" , "Mythical musician" , "Lyre player who could charm all living things" , "classical musician" .)