The Collaborative International Dictionary of English v.0.48:

Pouter \Pout"er\ (-[~e]r), n.
   1. One who, or that which, pouts.
      [1913 Webster]

   2. [Cf. E. pout, and G. puter turkey.] (Zool.) A variety of
      the domestic pigeon remarkable for the extent to which it
      is able to dilate its throat and breast.
      [1913 Webster]

WordNet (r) 3.0 (2006):

pouter
    n 1: someone with a habitually sullen or gloomy expression [syn:
         sourpuss, picklepuss, gloomy Gus, pouter]
    2: one of a breed of pigeon that enlarge their crop until their
       breast is puffed out [syn: pouter pigeon, pouter]