denumerable

The word was introduced around the beginning of the 20th century, from Latin denumerō (“to count out”) +‎ -able.

denumerable (not comparable)

1. (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.

   Synonyms: countable, countably infinite

   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.