Minuscule amount (4)
I believe the answer is:
iota
'minuscule amount' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for iota that I've seen before include "Ninth letter of Greek alphabet, small amount" , "Greek equivalent of the letter I" , "Just a jot, like Greek letter" , "Tiniest scrap" , "Smidgen" .)