Factor in a small amount (7)
I believe the answer is:
element
I believe this is a double definition.
'factor' is the first definition.
('element' can be a synonym of 'factor')
'a small amount' is the second definition.
(I've seen this before)
'in' acts as a link.
(Other definitions for element that I've seen before include "fire, perhaps, once" , "Eg, one dn" , "Constituent part (7)" , "Component of periodic table" , "Comfort zone" .)