aequus

Aequus is a Latin adjective meaning “even, level, equal, fair.” In Latin, it occurs in gendered forms such as aequus (masculine), aequa (feminine), and aequum (neuter), with the related noun aequitas meaning fairness or justice. The verb aequare means “to make equal,” and the noun aequatio can denote an equation or the act of making equal.

In classical Latin, aequus is used to describe both physical flatness and moral or juridical fairness. For example, a level surface may be described as aequus, while a person’s behavior could be praised for aequitas, or fairness. The term also underpins mathematical and practical ideas of equality, as reflected in related Latin terms such as aequatio (an equation or balancing).

The Latin root aequ- has had a lasting influence on many modern languages, especially English. It appears in a broad family of words tied to equality or balance, often through the form equ- or aequ- in English derivatives such as equate, equation, equal, equity, equator, and equinox (the latter from aequinoctium, meaning “equal night”). The semantic thread from aequus–aequitas to these terms centers on making things level, balanced, or just.

See also: Equation, Equal, Equity, Equator, Equinox.