alternated

Alternated is the past tense and past participle form of the verb alternate, meaning to occur in turn or to switch back and forth between two states. It can describe a sequence or pattern in which elements or conditions take turns, such as colors, days, or signals. For example, "The lights alternated between red and green," or "The workers alternated shifts." While "alternate" is more commonly used for present tense or as an adjective ("an alternating pattern"), "alternated" emphasizes a completed or repeated action in the past.

In mathematical or scientific writing, the related idea is often expressed with "alternating" rather than "alternated," as in "an alternating series" or "an alternating current." Nevertheless, "alternated" may appear when summarizing a past process that produced a two-state pattern, for instance, "The signs in the sequence alternated." The term is also used in scheduling or combinatorics to describe sequences that switch between two options.

Etymology: from Latin alternare, from alter meaning "the other." The form appears in English through Old French and Middle English influences.