Sun versus Echo: it's fast (6)
I believe the answer is:
'fast' is the definition.
(to fast is to refrain from eating food)
'sun versus echo' is the wordplay.
'sun' becomes 'star' (I've seen this in another clue).
'versus' becomes 'v'.
'echo' becomes 'e' (phonetic alphabet: alpha, bravo, charlie etc.).
'it's' acts as a link.
(Other definitions for starve that I've seen before include "Go without food" , "Suffer from food deprivation" , "Averts (anag)" , "Die from lack of food" , "Eat nothing" .)