The Collaborative International Dictionary of English v.0.48:

Sing \Sing\ (s[i^]ng), v. i. [imp. Sungor Sang; p. p.
   Sung; p. pr. & vb. n. Singing.] [AS. singan; akin to D.
   zingen, OS. & OHG. singan, G. singen, Icel. syngja, Sw.
   sjunga, Dan. synge, Goth. siggwan, and perhaps to E. say,
   v.t., or cf. Gr. ??? voice. Cf. Singe, Song.]
   1. To utter sounds with musical inflections or melodious
      modulations of voice, as fancy may dictate, or according
      to the notes of a song or tune, or of a given part (as
      alto, tenor, etc.) in a chorus or concerted piece.
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            The noise of them that sing do I hear. --Ex. xxxii.
                                                  18.
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   2. To utter sweet melodious sounds, as birds do.
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            On every bough the briddes heard I sing. --Chaucer.
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            Singing birds, in silver cages hung.  --Dryden.
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   3. To make a small, shrill sound; as, the air sings in
      passing through a crevice.
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            O'er his head the flying spear
            Sang innocent, and spent its force in air. --Pope.
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   4. To tell or relate something in numbers or verse; to
      celebrate something in poetry. --Milton.
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            Bid her . . . sing
            Of human hope by cross event destroyed. --Prior.
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   5. To cry out; to complain. [Obs.]
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            They should sing if thet they were bent. --Chaucer.
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The Collaborative International Dictionary of English v.0.48:

Singing \Sing"ing\,
   a. & n. from Sing, v.
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   Singing bird. (Zool.)
   (a) Popularly, any bird that sings; a song bird.
   (b) Specifically, any one of the Oscines.

   Singing book, a book containing music for singing; a book
      of tunes.

   Singing falcon or Singing hawk. (Zool.) See Chanting
      falcon, under Chanting.

   Singing fish (Zool.), a California toadfish (Porichthys
      porosissimus), called also midshipman; -- so called
      because it produces a buzzing sound with its air bladder.


   Singing flame (Acoustics), a flame, as of hydrogen or coal
      gas, burning within a tube and so adjusted as to set the
      air within the tube in vibration, causing sound. The
      apparatus is called also chemical harmonicon.

   Singing master, a man who teaches vocal music.

   Singing school, a school in which persons are instructed in
      singing.
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WordNet (r) 3.0 (2006):

singing
    adj 1: smooth and flowing [syn: cantabile, singing]
    n 1: the act of singing vocal music [syn: singing,
         vocalizing]
    2: disclosing information or giving evidence about another [syn:
       tattle, singing, telling]