c.1200, from Old Norse geta "to obtain, reach; to beget; to guess right" (past tense gatum, past participle getenn), from Proto-Germanic *getan (cf. Old Swedish gissa "to guess," literally "to try to get"), from PIE root *ghend- "seize, take" (cf. Greek khandanein "to hold, contain," Lithuanian godetis "be eager," second element in Latin prehendere "to grasp, seize," Welsh gannu "to hold, contain," Old Church Slavonic gadati "to guess, suppose"). Meaning "to seize mentally, grasp" is from 1892.
Old English, as well as Dutch and Frisian, had the root only in compounds (e.g. begietan "to beget," see