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' says the letters should be written backwards.
'to' in reverse letter order is '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" .)