Scrap answer after seeing nothing in it (4)
I believe the answer is:
iota
'scrap' is the definition.
(both can mean a very small amount)
'answer after seeing nothing in it' is the wordplay.
'answer' becomes 'a' (abbreviation eg in Q and A).
'after' means one lot of letters go next to another.
'seeing nothing' becomes 'O' (O resembles 0).
'in' is an insertion indicator.
'o' going inside 'it' is 'iot'.
'a' put after 'iot' is 'IOTA'.
(Other definitions for iota that I've seen before include "(Not one) little bit" , "Tiny bit" , "Hint" , "Smidgeon" , "Foreign character" .)