"well-off, having much money, in good circumstances;" also "well-equipped," 1872, American English slang (originally in the "money" sense), from well, adv. + colloquial sense of heeled. "[A]pplied to a player at cards who has a good hand, to a person who possesses plenty of money, or to a man who is well armed" [Century Dictionary]. From 1817 in a literal sense, in reference to shoes.