The Collaborative International Dictionary of English v.0.48:

Puck \Puck\, n. [OE. pouke; cf. OSw. puke, Icel. p[=u]ki an evil
   demon, W. pwca a hobgoblin. Cf. Poker a bugbear, Pug.]
   1. (Medi[ae]val Myth.) A celebrated fairy, "the merry
      wanderer of the night;" -- called also Robin Goodfellow,
      Friar Rush, Pug, etc. --Shak.
      [1913 Webster]

            He meeteth Puck, whom most men call
            Hobgoblin, and on him doth fall.      --Drayton.
      [1913 Webster]

   2. (Zool.) The goatsucker. [Prov. Eng.]
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Robin Goodfellow \Rob"in Good"fel`low\
   A celebrated fairy; Puck. See Puck. --Shak.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Robin Goodfellow
    n 1: a mischievous sprite of English folklore [syn: Puck,
         Robin Goodfellow]