- Old English þe (accusative and dative singular of þu "thou"), from Proto-Germanic *theke (cf. Old Frisian thi, Middle Dutch di, Old High German dih, German dich, Old Norse þik, Norwegian deg, Gothic þuk), from PIE *tege-. A brief history of the second person pronoun in English can be found here. The verb meaning "to use the pronoun 'thee' to someone" is recorded from 1662, from the rise of Quakerism (see thou).
This was the Bottom upon which the Quakers first set up, to run down all worldly Honour ...; to Thee and Thou; to call no Man Master, or Lord, and not to take off their Hats, or Bow to any. [Charles Leslie, "The Snake in the Grass," 1696]