Thesaurus

(adj) : being or succeeding by turns; one following the other in succession of time or place; by turns first one and then the other; hence, reciprocal; designating the members in a series, which regularly intervene between the members of another series, as the odd or even numbers of the numerals; every other; every second

(n) : that which alternates with something else; vicissitude; (Misuse) A substitute; an alternative; one designated to take the place of another, if necessary, in performing some duty

(v) : to perform by turns, or in succession; to cause to succeed by turns; to interchange regularly; to happen, succeed, or act by turns; to follow reciprocally in place or time;—followed by with; as, the flood and ebb tides alternate with each other