nub /nʌb/ BrE AmE noun
[ Date: 1500-1600 ; Origin: Probably from Low German knubbe ]
1 . the nub of the problem/matter/argument etc the main point of a problem etc:
The real nub of the matter is money.
2 . [countable] a small rounded piece of something, especially a piece that is left after the rest has been eaten, used etc