It's very little for one to get ahead with (3)
I believe the answer is:
ion
'it's very little' is the definition.
I can't judge whether this defines the answer.
'one to get ahead with' is the wordplay.
I cannot really understand how this works, but
'one' could be 'i' (Roman numeral) and 'i' is located in the answer.
'ahead' could be 'on' (synonyms) and 'on' is found within the answer.
This accounts for all the letters.
This explanation may well be incorrect...
'for' is the link.
Can you help me to learn more?
(Other definitions for ion that I've seen before include "Charged atom/molecule" , "Electrically charged particle" , "Particle (phys.)" , "Subatomic particle" , "Eletrically charged particle" .)