Numerus

Numerus is a Latin noun meaning "number" or "sum." It also denotes a pattern or quantity and is the historical source of many English terms such as number, numeral, and numerous. In Roman and medieval usage, numerus appears as both a mathematical concept and a grammatical category.

In grammar, numerus describes the category of number, typically singular and plural. Latin grammar requires agreement in numerus between nouns, adjectives, and verbs; discussions of numerus appear in traditional grammar as a core feature of syntax. Some languages have more numeri, but Latin historically uses two values.

In mathematics and philosophy, numerus designates the abstract notion of a number, as in texts on arithmetic and number theory. Medieval and early modern Latin authors used numerus to discuss natural numbers and other numeric concepts.

In law and society, numerus appears in phrases such as numerus clausus, a term adopted into several languages to denote a restricted or fixed number of entrants or positions.

In the Roman military, numerus referred to a unit or corps within the auxilia, often composed of non-citizen soldiers and led by a centurion, functioning similarly to an auxiliary cohort or ala in certain periods.