crux.

The decisive problem or essential point on which an issue turns.

Use it for

Words that belong together

• the crux of the matter
• the central crux
• an interpretive crux

On the page

The crux was not whether the letter was genuine, but why it had arrived thirty years late.

One damaged verb became the crux of her reading of the manuscript.

Usage notes

Primary category: literary. Forms: Singular crux; plural cruxes. Legacy lexical fields mirror sense 1 only. Use numbered sense fields for all meanings.