I turn to a small amount (4)
I believe the answer is:
iota
'small amount' is the definition.
(I've seen this in another clue)
'i turn to a' is the wordplay.
'turn' shows that the letters should be reversed in order.
'to' backwards is 'ot'.
'i'+'ot'+'a'='IOTA'
(Other definitions for iota that I've seen before include "Foreign character" , "Greek letter; tiny amount" , "(Not one) little bit" , "European letter" , "Greek letter of little value" .)