nub
noun /nʌb/
/nʌb/
[singular]- the nub (of something) the central or essential point of a situation, problem, etc.
- The nub of the matter is that business is declining.
- She’s too selfish to help. That’s the nub.
Word Originlate 17th cent.: apparently a variant of dialect knub ‘protuberance’, from Middle Low German knubbe, knobbe ‘knob’.