The word thou (pronounced IPA [ðaʊ]) is mostly archaic, functioning as the second person singular pronoun in English and having been replaced in almost all contexts by you. Thou is the nominative form; the oblique/objective form is thee (functioning as both accusative and dative), and the possessive is thy or thine. Almost all verbs following "thou" have the endings -st or -est; e.g., "thou goest". In Middle English, thou was sometimes abbreviated by writing a Wynn-shaped letter Thorn with a small u above it.
Originally, "thou" was simply the singular counterpart to the plural pronoun "ye," descended from an ancient Indo-European root. In imitation of the French practice, "thou" was later used to express intimacy, familiarity, or even disrespect while another pronoun, "you" was used for formal circumstances. See French "vous" and Dutch "U". After "thou" fell out of fashion, it was primarily retained in fixed rituals, so that it eventually came to connote formality and solemnity. "Thou" persists, sometimes in altered form, in regional dialects of England and Scotland.