sempiternal UK /ˌsɛm.pɪˈtɜː.nəl/US /ˌsɛm.pɪˈtɝ.nəl/ adjective2 •Everlasting, eternal.Why not sempiternal / Thou and I? Our vernal / Brightness keeping, / Time outleaping: / Passed the hodiernal! — 1898 •Having infinite temporal duration, rather than outside time and thus lacking temporal duration altogether; everlasting.