adj

• Happening by turns; one following the other in succession of time or place; first one and then the other (repeatedly).
  "Goldschmidt (Austria; creation July 27, 1862): [...] party, argent and gules, an eagle of alternate colors, [...]"
• (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.
  "the alternate members 1, 3, 5, 7, etc."
• (US) Other; alternative.
  "Hyperlinked text is displayed in alternate color in a Web browser."
• (botany, of leaves) Distributed singly at different heights of the stem, and at equal intervals as respects angular divergence
  "Many trees have alternate leaf arrangement (e.g. birch, oak and mulberry)."

noun

• (US) A substitute; an alternative; one designated to take the place of another, if necessary, in performing some duty.
  "Corridors beyond this point have collapsed. I'm looking for an alternate. Careful."
• (mathematics) A proportion derived from another proportion by interchanging the means.
• (US) A replacement of equal or greater value or function.

verb

• (transitive) To perform by turns, or in succession; to cause to succeed by turns; to interchange regularly.
  "The most high God, in all things appertaining unto this life, for sundry wise ends alternates the disposition of good and evil."
• (intransitive) 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."
• (intransitive) To vary by turns.
  "The land alternates between rocky hills and sandy plains."
• (transitive, geometry) To perform an alternation (removal of alternate vertices) on (a polytope or tessellation); to remove vertices (from a face or edge) as part of an alternation.
  "This case suggests that the alternation of a polyhedron should be bounded by actual vertex figures and alternated faces. The case of the cube is in agreement with this notion, since the alternated square is nothing."