Crossword Genius

You'll need another one to make one (4)

Ross

I believe the answer is:

half

I'm a little stuck... Click here to teach me more about this clue!

'one' is the definition.
The answer and definition can be both quantities as well as being singular nouns.
Perhaps they are linked in a way I don't understand?

I don't understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for half that I've seen before include "Measure of beer" , "Wife the better one (joc.)" , "50 per cent" , "Short distance - steal!" , "alcoholic drink" .)

I've seen this clue in The Globe and Mail.
Want a hint initially instead of a full solution? Install my app