Combines numbers as it makes sense (4,2)
I believe the answer is:
adds up
'makes sense' is the definition.
('add up' can be a synonym of 'make sense')
'combines numbers as it' is the wordplay.
I cannot really understand how this works, but
'combines' could be 'adds' (I've seen this in another clue) and 'adds' is located in the answer.
The remaining letters 'up' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for adds up that I've seen before include "Puts two and two together" , "Stands to reason" , "Reckons" , "Tots" , "Totals" .)