For all intents and purposes, alternate and alternative are synonymous. Both words date to the middle of the 16th century, and both describe a choice apart from what is first offered: an alternate viewpoint; an alternative suggestion.

As a noun, alternate (the last syllable rhymes with "net") refers to a substitute—someone who is prepared to take the place of someone else. As an adjective, "alternate" (again, the last syllable rhymes with "net") means occurring by turns or being one of two or more choices.

An alternate is something or someone that serves in place of another. An alternative is a second option that does not replace the first.

Alternate (ly), alternative (ly) The adjective alternate and the adverb alternately mean ‘first one thing, then another thing and then the first thing again’.