tame curse word, 1781, American English euphemism, a minced form of damn said to have originated in New England when swearing was a punishable offense; if so, its spread probably was influenced by 'tarnal, short for Eternal, as in By the Eternal (God), favorite exclamation of Andrew Jackson, among others (see tarnation). Mark Twain (who spells it dern) writes “this imprecation is a favorite one out in the ranching districts, and is generally used in the society of ladies, where a mild firm of expressionomy may be indulged in” (San Francisco, 1865). Related: darned (as a past-participle adjective, 1806); darndest (superlative, 1844), darnation (noun of action, 1798).
also *ayu-, Proto-Indo-European root meaning "vital force, life; long life, eternity."
It forms all or part of: age; aught (n.1) "something; anything;" aye (adv.) "always, ever;" Ayurvedic; coetaneous; coeval; each; eon; eternal; eternity; ever; every; ewigkeit; hygiene; longevity; medieval; nay; never; no; primeval; sempiternal; tarnation; utopia.
It is the hypothetical source of/evidence for its existence is provided by: Sanskrit ayu- "life;" Avestan aiiu "age, life(time);" Greek aiōn "age, vital force; a period of existence, a lifetime, a generation; a long space of time," in plural, "eternity;" Latin aevum "space of time, eternity;" Gothic aiws "age, eternity," Old Norse ævi "lifetime," German ewig "everlasting," Old English a "ever, always."