From Longman Dictionary of Contemporary Englishthe nub of the problem/matter/argument etcthe nub of the problem/matter/argument etcMAINthe main point of a problem etc The real nub of the matter is money. → nub
Examples from the Corpus
the nub of the problem/matter/argument etc• Even so, some brain cells were still working, as I stared inwardly at the nub of the problem.• It sounds perfectly reasonable, but you will perceive that here is the nub of the matter.• This is the nub of the matter.• This, however, was the nub of the problem. 