ˈkrəks also -ru̇ks noun
( plural cruxes -ksə̇z ; also cru·ces ˈkrüˌsēz)
Etymology: Latin, cross, torture — more at ridge
1.
a. : a puzzling, confusing, or difficult problem : an unsolved question
a scholarly crux about the meaning of a line in Shakespeare
b. : a determinative point at issue : a pivotal or essential point requiring resolution or resolving an outcome
the crux of the problem
2. : a main or central feature (as of an argument or plan)
he discarded all but the essential cruxes of his argument — Carl Van Doren