Borrowed from Latin alternus (“every other, alternate”).

altern (not comparable)

1. (obsolete) Acting by turns; alternate.
   • 1667, John Milton, “Book CLXXXIX”, in Paradise Lost.[…], London: […] [Samuel Simmons], and are to be sold by Peter Parker[…]; [a]nd by Robert Boulter[…]; [a]nd Matthias Walker,[…], →OCLC; republished as Paradise Lost in Ten Books:[…], London: Basil Montagu Pickering[…], 1873, →OCLC, lines 346-352:

     And God made two great lights, great for thir use / To Man, the greater to have rule by day, / The less by night, alterne ; and made the stars, / And set them in the firmament of Heaven / To illuminate the Earth, and rule the day / In their vicissitude, and rule the night, / And light from darkness to divide. […]

• altern base

• Antler, Lenart, antler, learnt, rental, ternal

From Middle High German altern, from Old High German *altarōn (only attested as the past participle gialdaroda), from Proto-West Germanic *aldarōn.

• IPA^(key): /ˈʔaltɐn/

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altern (weak, third-person singular present altert, past tense alterte, past participle gealtert, auxiliary sein)

1. to age

• Altern
• Alterung

• “altern” in Digitales Wörterbuch der deutschen Sprache
• “altern” in Uni Leipzig: Wortschatz-Lexikon
• “altern” in Duden online
• “altern” in OpenThesaurus.de

Borrowed from French alterne, from Latin alternus.

altern m or n (feminine singular alternă, masculine plural alterni, feminine/neuter plural alterne)

1. alternate