The Collaborative International Dictionary of English v.0.48:

Nightingale \Night"in*gale\, n. [OE. nihtegale,nightingale, AS.
   nihtegale; niht night + galan to sing, akin to E. yell; cf.
   D. nachtegaal, OS. nahtigala, OHG. nahtigala, G. nachtigall,
   Sw. n[aum]ktergal, Dan. nattergal. See Night, and Yell.]
   1. (Zool.) A small, plain, brown and gray European song bird
      (Luscinia megarhynchos syn. Luscinia luscinia). It
      sings at night, and is celebrated for the sweetness of its
      song.
      [1913 Webster]

   2. (Zool.) A larger species (Lucinia philomela), of Eastern
      Europe, having similar habits; the thrush nightingale. The
      name is also applied to other allied species.
      [1913 Webster]

   Mock nightingale. (Zool.) See Blackcap, n., 1
      (a) .
          [1913 Webster]

WordNet (r) 3.0 (2006):

Luscinia megarhynchos
    n 1: European songbird noted for its melodious nocturnal song
         [syn: nightingale, Luscinia megarhynchos]