The Collaborative International Dictionary of English v.0.48:

Smew \Smew\, n. [Perhaps for ice-mew.] (Zool.)
   (a) small European merganser (Mergus albellus) which has a
       white crest; -- called also smee, smee duck, white
       merganser, and white nun.
   (b) The hooded merganser. [Local, U.S.]
       [1913 Webster]

WordNet (r) 3.0 (2006):

Mergus albellus
    n 1: smallest merganser and most expert diver; found in northern
         Eurasia [syn: smew, Mergus albellus]