crux

¹ American  

[kruhks] / krʌks /

noun

plural

cruxes, cruces

1. a vital, basic, decisive, or pivotal point.

   The crux of the trial was his whereabouts at the time of the murder.

   Synonyms:

   gist, core, heart, essence

2. a cross.

3. something that torments by its puzzling nature; a perplexing difficulty.

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Crux ² American  

[kruhks] / krʌks /

noun

Astronomy.

genitive

Crucis

1. Southern Cross.

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crux ¹ British  

/ krʌks /

noun

1. a vital or decisive stage, point, etc (often in the phrase the crux of the matter )

2. a baffling problem or difficulty

3. mountaineering the most difficult and often decisive part of a climb or pitch

4. a rare word for cross

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Crux ² British  

/ krʌks /

noun

1. the more formal name for the Southern Cross

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Etymology

Origin of crux¹

1635–45; < Latin: stake, scaffold, or cross used in executions, torment; figurative senses perhaps < New Latin crux ( interpretum ) (commentators') torment, a difficult passage in a text; crucial

Origin of Crux²

< Latin: a cross

Example Sentences

The crux of his argument is better-than-anticipated industry pricing in the first quarter, which “has seemingly moved well ahead of expectations set previously by Micron.”

From Barron's • Mar. 13, 2026

At the crux of the case was whether Rogers knowingly attempted to advance China’s interests or was unwittingly duped into providing information to spies he thought were academics.

From The Wall Street Journal • Feb. 3, 2026

The crux of the issue is that she paid for work on a trust-owned asset before she legally owned it, which is not the same thing as a buyer upgrading their own home.

From MarketWatch • Jan. 19, 2026

And this is the crux of the matter.

From BBC • Jan. 6, 2026

Thus, conceivably the crux of the matter was a rule governing hydrogen bonding between bases.

From "Double Helix" by James D. Watson

Related Words

• bottom line
• core
• essence
• gist
• nub