I return to a small amount (4)
I believe the answer is:
iota
'small amount' is the definition.
(I've seen this in another clue)
'i return to a' is the wordplay.
'return' shows that the letters should be reversed in order.
'to' written backwards gives 'ot'.
'i'+'ot'+'a'='IOTA'
(Other definitions for iota that I've seen before include "Ninth letter of Greek alphabet, small amount" , "Smidgeon" , "Smidgen" , "very small part" , "Jot, particle" .)