See Hebrews 6:1–2; and New Testament Revision 2, part 2, p. 139 [Joseph Smith Translation, Hebrews 6:1–2].
Gnolaum, or ‘olam, is a Hebrew noun defined as “eternity” or “a long period” (referring to “time to come or to time past”). The word is used and defined as the adjective “eternal” in the Book of Abraham, which JS published in 1842. (Gibbs, Manual Hebrew and English Lexicon, 160; Book of Abraham Excerpt and Facsimile 2, 15 Mar. 1842 [Abraham 3:18].)
Gibbs, Josiah W. A Manual Hebrew and English Lexicon Including Biblical Chaldee. Designed Particularly for Beginners. 2nd ed. New Haven, CT: Hezekiah Howe, 1832.