Definition of alternate:
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
"and bid alternate passions fall and rise. -Pope"
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
"grateful alternates of substantial. -Prior"
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