Etymology

Betti number

Today it means: Any of a sequence of numbers, denoted bₙ, which characterise a given topological space K by giving, for each dimension, the number of holes in K of said dimension; (formally) the rank of the nth homology group, Hₙ, of K. Full definition →

French nombre de Betti
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The story

  1. French · derived fromnombre de Betti
  2. English todayBetti number

A calque of French nombre de Betti, coined in 1892 by Henri Poincaré; named after Italian mathematician Enrico Betti in recognition of an 1871 paper.

Etymology from Wiktionary, CC BY-SA 4.0.