1610s, from Late Latin longaevitatem (nominative longaevitas) "great age, long life," from Latin longaevus "of great age, ancient, aged," from longus "long" (see long (adj.)) + aevum "lifetime, age" (from PIE root *aiw- "vital force, life; long life, eternity").

"always, ever," c. 1200, from Old Norse ei "ever" (cognate with Old English a "always, ever"), from Proto-Germanic *aiwi-, extended form of PIE root *aiw- "vital force, life; long life, eternity" (source also of Greek aiōn "age, eternity," Latin aevum "space of time").

"having the same age, having lived for an equal period," 1620s, from Late Latin coaevus"of the same age," from assimilated form of Latin com "with, together" (see com-) + aevum "an age" (from PIE root *aiw- "vital force, life; long life, eternity"). As a noun from c. 1600.

also primaeval, "of or belonging to the first age," 1650s, with -al (1) + Latin primaevus "early in life, youthful," from primus "first" (see prime (adj.)) + aevum "an age" (from PIE root *aiw- "vital force, life; long life, eternity"). Related: Primevally.

"pertaining to life," 1847, also biotical (1847), from Latin bioticus, from Greek biotikos "pertaining to life," from bios "life," from PIE root *gwei- "to live." Biotic factor was in use by 1907. Related: Biotical. Biotics "science of vital functions and manifestations; powers and qualities peculiar to living organisms" (T. Sterry Hunt) is from 1882.

word of negation or refusal, "no" as a reply to a question, late 12c., from a Scandinavian source such as Old Norse nei, compound of ne "not" (from PIE root *ne- "not") + ei "ever," from Proto-Germanic *aiwi-, extended form of PIE root *aiw- "vital force, life; long life, eternity."

"having the same age as another, beginning to exist at the same time," c. 1600, from Late Latin coaetanus "one of the same age," from assimilated form of Latin com "with, together with" (see com-) + aetas "age" (from PIE root *aiw- "vital force, life; long life, eternity") + adjectival suffix -aneus. Related: Coetaneously.

early 15c., "without vital force, having lost life," from Late Latin inanimatus "lifeless," from in- "not" (see in- (1)) + animatus (see animation). The Latin word closest corresponding in form and sense is inanimalis. Meaning "lacking vivacity, without spirit, dull" is from 1734. Inanimate as a verb meant "infuse with life or vigor" (17c.), from the other in- (see in- (2)).

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."  

late 14c., "quality of being eternal," from Old French eternité "eternity, perpetuity" (12c.), from Latin aeternitatem (nominative aeternitas), from aeternus "enduring, permanent," contraction of aeviternus "of great age," from aevum "age" (from PIE root *aiw- "vital force, life; long life, eternity").  Meaning "infinite time" is from 1580s. In the Mercian hymns, Latin aeternum is glossed by Old English ecnisse.