Source : Webster's Revised Unabridged Dictionary (1913)

Berceuse \Ber`ceuse"\, n. [F.] (Mus.)
   A vocal or instrumental composition of a soft tranquil
   character, having a lulling effect; a cradle song.

Source : WordNet®

berceuse
     n : a quiet song intended to lull a child to sleep [syn: {lullaby},
          {cradlesong}]