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Eternal, endless.

It comes from Latin semper (always) and aeternus (eternal).
Time is sempiternal.
by Sempiternal January 03, 2010
Eternal and Everlasting; also coincidentally the name of the latest Bring Me The Horizon album. The title comes from a line in the song, "THIS IS SEMPITERNAL, WILL WE EVER SEE THE END? THIS IS SEMPITERNAL, OVER AND OVER AGAIN AND AGAIN."

Also a common joke that it is really "sandpit turtle".....it isn't
boy: "Wow, that new BMTH album is really good!"
friend: "Yeah, I love sempiternal!"

teacher: "They saw that knowledge is eternal."
other teacher: "indeed, it is sempiternal!"
by jessica sky June 16, 2013