a vital, basic, decisive, or pivotal point

The crux of the trial was his whereabouts at the time of the murder.

a cross.

something that torments by its puzzling nature; a perplexing difficulty.

noun

trivia

noun

body , bottom line * , core , decisive point , essence , gist , heart , kernel , matter , meat * , meat and potatoes * , nitty-gritty , nub , pith , purport , substance , thrust , basis , cross , crunch , difficulty , meat , moment , point , problem , puzzle , puzzling , riddle