- is third person singular present of be, O.E. is, from Germanic stem *es- (Cf. O.H.G., Ger., Goth. ist, O.N. es, er), from PIE *es-ti- (Cf. Skt. asti, Gk. esti, L. est, Lith. esti, O.C.S. jesti), from PIE root *es- "to be." O.E. lost the final -t-. See BE (Cf. be). Until 1500s, pronounced to rhyme with kiss.
Etymology dictionary. 2014.