I return to a tiny amount (4)
I believe the answer is:
iota
'tiny amount' is the definition.
(I've seen this before)
'i return to a' is the wordplay.
'return' is a reversal indicator.
'to' in reverse letter order is 'ot'.
'i'+'ot'+'a'='IOTA'
(Other definitions for iota that I've seen before include "Smidgeon" , "letter from abroad" , "Contrivance" , "Greek equivalent of the letter I" , "Old letter" .)