I'd pronounce it with "Etern-uh-tus. (With similar pronunciation to "eternal".)

E-ter-nuh-tis

ee-tur-naa-tus

E-turn-nee-us

"Ee-Turn-Uh-tiss"

Et-tern-nuh-tis

Ee-ter-nuh-tis

Is E prounounsed ee or eh

@Frostthecatto

E-ter-nah-tis