alternate

Happening by turns; one following the other in succession of time or place; first one and then the other (repeatedly)

(mathematics) 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.

(US) Other; alternative.

(botany, of leaves) Distributed singly at different heights of the stem, and at equal intervals as respects angular divergence