ETYM Latin, cross, torture, trouble.
The most important point; SYN. crux of the matter.
1. A puzzling or difficult problem; an unsolved question.
2. An essential point requiring resolution or resolving an outcome.
3. A main or central feature (as of an argument).

Constellation of the southern hemisphere, popularly known as the Southern Cross, the smallest of the 88 constellations. Its brightest stars are Alpha Crucis (or Acrux), a double star about 400 light-years from Earth, and Beta Crucis (or Mimosa). Near Beta Crucis lies a glittering star cluster known as the Jewel Box. The constellation also contains the Coalsack, a dark cloud of dust silhouetted against the bright starry background of the Milky Way.