Upward spin for eye (4)
I believe the answer is:
leer
'for eye' is the definition.
(I've seen this in another clue)
'upward spin' is the wordplay.
'upward' shows that the letters should be reversed in order (in a down clue, letters go up).
'spin' becomes 'reel' (synonyms).
'reel' back-to-front is 'LEER'.
(Other definitions for leer that I've seen before include "Stare suggestively" , "Lecherous look" , "Look lecherously" , "unpleasant look" , "Look suggestively" .)