I wish I fly on wind (2,4)
I believe the answer is:
if only
'i wish' is the definition.
(I've seen this before)
'i fly on wind' is the wordplay.
'wind' indicates an anagram.
'fly'+'on'='flyon'
'flyon' is an anagram of 'fonly'.
'i'+'fonly'='IF ONLY'
(Other definitions for if only that I've seen before include "I wish that could be provided just after" , "Would that" , "in my dreams" , "expression of wish" .)