alternate (v.) Look up alternate at Dictionary.com
1590s, from Latin alternatus, past participle of alternare (see alternate (adj.)). Replaced Middle English alternen "to vary, alternate" (early 15c.). Related: Alternated; alternating.
alternate (n.) Look up alternate at Dictionary.com
1718, "that which alternates (with anything else)," from alternate (adj.). Meaning "a substitute" is first attested 1848.
alternate (adj.) Look up alternate at Dictionary.com
1510s, from Latin alternatus "one after the other," past participle of alternare "to do first one thing then the other; exchange parts," from alternus "one after the other, alternate, in turns, reciprocal," from alter "the other" (see alter). Alternate means "by turns;" alternative means "offering a choice." Both imply two kinds or things.