third person singular present of be, Old English is, from Germanic stem *es- (cf. Old High German, German, Gothic ist, Old Norse es, er), from PIE *es-ti- (cf. Sanskrit asti, Greek esti, Latin est, Lithuanian esti, Old Church Slavonic jesti), from PIE root *es- "to be." Old English lost the final -t-. See be. Until 1500s, pronounced to rhyme with kiss.