crux

noun5

1. •
   The basic, central, or essential point or feature.

   • The crux of her argument was that the roadways needed repair before anything else could be accomplished.
2. •
   The critical or transitional moment or issue, a turning point.

   • The movie hits its dramatic crux an hour in, when Reality [Winner], at work at the contractor’s facility in Georgia, discovers what she deems a tragic scandal. — 2024
3. •
   A puzzle or difficulty.

   • What I have advanced upon this species of verse will contribute to solve a poetical problem, thrown out by Dryden as a crux to his brethren — 1775
4. •
   The hardest point of a climb.

   • the real crux of the climb was encountered — 1907
5. •
   A cross on a coat of arms.