Etymology

Adjective

1. 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.

   And bid alternate passions fall and rise. -Alexander Pope

2. 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.

   the alternate members 1, 3, 5, 7, etc.

3. Other or alternative.
4. Distributed, as leaves, singly at different heights of the stem, and at equal intervals as respects angular divergence. --Gray.

Noun

1. That which alternates with something else; vicissitude.

   Grateful alternates of substantial. -Matthew Prior

2. A substitute; an alternative; one designated to take the place of another, if necessary, in performing some duty.
3. A proportion derived from another proportion by interchanging the means.
4. A replacement of equal or greater value or function.
5. Figures or tinctures that succeed each other by turns.

Verb

1. To perform by turns, or in succession; to cause to succeed by turns; to interchange regularly.
2. To happen, succeed, or act by turns; to follow reciprocally in place or time;—followed by with.

   The flood and ebb tides alternate with each other.

3. To vary by turns.

   The land alternates between rocky hills and sandy plains.