1877, from German, literally "eternity," from ewig "everlasting" (from PIE root *aiw- "vital force, life; long life, eternity") + -keit word-forming element meaning "state or condition of being" (see -hood).
Entries linking to ewigkeit
*aiw-
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."
-hood
word-forming element meaning "state or condition of being," from Old English -had "condition, quality, position" (as in cildhad "childhood," preosthad "priesthood," werhad "manhood"), cognate with German -heit/-keit, Dutch -heid, Old Frisian and Old Saxon -hed, all from Proto-Germanic *haidus "manner, quality," literally "bright appearance," from PIE (s)kai- (1) "bright, shining" (Cognates: Sanskrit ketu "brightness, appearance"). Originally a free-standing word (see hade); in Modern English it survives only in this suffix.