What does "cross-ratio" mean?

A special number associated with an ordered quadruple of collinear points, particularly points on a projective line, and preserved by the fractional linear transformations.

What is a synonym for "cross-ratio"?

Common synonyms include: anharmonic ratio, double ratio.

Cross-ratio

noun

noun ·Rare ·Advanced level

Definitions

Noun

1
A special number associated with an ordered quadruple of collinear points, particularly points on a projective line, and preserved by the fractional linear transformations.

Synonyms

All synonyms

anharmonic ratio double ratio

Etymology

From cross- + ratio.

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Data sourced from Wiktionary, WordNet, CMU, and other open linguistic databases. Updated March 2026.