Nevertheless, it makes sense, to a man (6)
I believe the answer is:
Here is my best explanation:
'nevertheless' is the definition.
('withal' can be a synonym of 'nevertheless')
'it makes sense to a man' is the subsidiary indication.
'it makes sense' becomes 'wit' (I can't explain this - if you can you should give a lot more credence to this answer).
'to a man' becomes 'hal' (I've seen this before).
(Other definitions for withal that I've seen before include "In addition (archaic)", "it's all the same to Shakespeare", "nevertheless", "Despite that, notwithstanding", "moreover", "To boot" and "as well".)