The Collaborative International Dictionary of English v.0.48:

Wren \Wren\ (r[e^]n), n. [OE. wrenne, AS. wrenna, wr[ae]nna,
   perhaps akin to wr[=ae]ne lascivious.]
   [1913 Webster]
   1. (Zool.) Any one of numerous species of small singing birds
      belonging to Troglodytes and numerous allied of the
      family Troglodytidae.
      [1913 Webster]

   Note: Among the species best known are the house wren
         (Troglodytes aedon) common in both Europe and
         America, and the American winter wren (Troglodytes
         hiemalis). See also Cactus wren, Marsh wren, and
         Rock wren, under Cactus, Marsh, and Rock.
         [1913 Webster]

   2. (Zool.) Any one of numerous species of small singing birds
      more or less resembling the true wrens in size and habits.
      [1913 Webster]

   Note: Among these are several species of European warblers;
         as, the reed wren (see Reed warbler
      (a), under Reed), the sedge wren (see Sedge warbler,
          under Sedge), the willow wren (see Willow warbler,
          under Willow), the golden-crested wren, and the
          ruby-crowned wren (see Kinglet).
          [1913 Webster]

   Ant wren, any one of numerous South American birds of the
      family Formicaridae, allied to the ant thrushes.

   Blue wren, a small Australian singing bird (Malurus
      cyaneus), the male of which in the breeding season is
      bright blue. Called also superb warbler.

   Emu wren. See in the Vocabulary.

   Wren babbler, any one of numerous species of small timaline
      birds belonging to Alcippe, Stachyris, Timalia, and
      several allied genera. These birds are common in Southern
      Asia and the East Indies.

   Wren tit. See Ground wren, under Ground.

   Wren warbler, any one of several species of small Asiatic
      and African singing birds belonging to Prinia and allied
      genera. These birds are closely allied to the tailor
      birds, and build their nests in a similar manner. See also
      Pincpinc.
      [1913 Webster]

WordNet (r) 3.0 (2006):

Troglodytes aedon
    n 1: common American wren that nests around houses [syn: house
         wren, Troglodytes aedon]