sempiternal

Despite their similarities, sempiternal and eternal come from different roots. Sempiternal is derived from the Late Latin sempiternalis and ultimately from semper, Latin for "always." (You may recognize semper as a key element in the motto of the U.S. Marine Corps: semper fidelis, meaning "always faithful.") Eternal, on the other hand, is derived, by way of Middle French and Middle English, from the Late Latin aeternalis and ultimately from aevum, Latin for "age" or "eternity." Sempiternal is much less common than eternal, but some writers have found it useful. 19th-century American writer Ralph Waldo Emerson, for example, wrote, "The one thing which we seek with insatiable desire is to forget ourselves, … to lose our sempiternal memory, and to do something without knowing how or why…."