What is the Latin word for eternally?

The usual Latin words for “eternally” are perpetuus, semper. The right choice depends on the sense; see the distinctions below.

English → Latin

“eternally” in Latin

perpetuusperpetual, everlasting, continuous, uninterrupted, constant, incessant, unbroken; ablative of time: a duration of time, semperalways, ever, forever, at all times, on each occasion, ongoing, constant

Riddle & Arnold A Copious and Critical English–Latin Lexicon, 1864

eternally

perpetuo (perpetually, continually); semper (always): numquam non (never not): to live eternally, in aeternum vivere, aeternum esse, sempiterna frui vita, perpetua vita perfrui, aevo sempiterno frui (all of continuance after death, the latter rather poetical); vigere memoria saeculorum omnium; per omnium saeculorum memoriam vivere; manere in animis hominum, in aeternitate temporum, fama rerum (IMPROP., to live forever in the memory of mankind; the latter, Tac., Agr., 46, extr.): to last eternally, durare in aeternum (Quint.).

Quick answer

What is the Latin word for eternally?: The usual Latin words for “eternally” are perpetuus, semper. The right choice depends on the sense; see the distinctions below.

Entry from J. E. Riddle & T. K. Arnold, A Copious and Critical English–Latin Lexicon (rev. C. Anthon, New York: Harper, 1864), digitised by Fergus J. P. Walsh, CC BY-SA 4.0; Latin markup adapted by latindictionary.co.