What does "thou" mean?

Thou: Note: "In Old English, generally, thou is the language of a lord to a servant, of an equal to an equal, and expresses also companionship, love, permission, defiance, scorn, threatening: whilst ye is the language of a servant to a lord, and of compliment, and further expresses honor, submission, or entreaty." Skeat. Note: Thou is now sometimes used by the Friends, or Quakers, in familiar discourse, though most of them corruptly say thee instead of thou.