n.
Pronunciation: ' kr ə ks, ' kru ̇ ks
Function: noun
Inflected Form: plural crux · es also cru · ces \ ' krü- ˌ s ē z \
Etymology: Latin cruc-, crux cross, torture
Date: 1718
1 : a puzzling or difficult problem : an unsolved question
2 : an essential point requiring resolution or resolving an outcome <the crux of the problem>
3 : a main or central feature (as of an argument)