The word is used since the beginning of the 20th century in Mathematics. It has been built from the Latin verb denumerare meaning to count out.
denumerable (not comparable)
- (mathematics) Capable of being assigned a bijection to the natural numbers. Applied to sets which are not finite, but have a one-to-one mapping to the natural numbers.
- The empty set is not denumerable because it is finite; the rational numbers are, surprisingly, denumerable because every possible fraction can be assigned a natural number and vice versa.