One gets nothing for it (3)
I believe the answer is:
ten
'one' is the definition.
The definition and answer can be both quantities as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'nothing for it' is the wordplay.
'nothing' becomes 'en' (I can't explain this - if you can you should give a lot more credence to this answer).
'for' means one lot of letters go next to another (I've seen this in other clues).
'it' becomes ''t' (abbreviation. e.g. in 'tis).
'en' put after 't' is 'TEN'.
'gets' acts as a link.
(Other definitions for ten that I've seen before include "X-WORD" , "Half a score" , "honour" , "Base of decimal system" , "Very young" .)