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.
      [1913 Webster]

            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.
   [1913 Webster]

   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]

Moby Thesaurus II by Grady Ward, 1.0:

86 Moby Thesaurus words for "singing":
   alto, baritone, bass, beaming, beatific, beatified, bel canto,
   blessed, blissful, bravura, capering, cheerful, chirping, choral,
   choral service, choral singing, choric, coloratura, croon,
   crooning, dancing, dramatic, eisteddfod, falsetto,
   farewell performance, flushed with joy, folk singing,
   folk-music festival, folk-sing, gay, glad, glowing, happy, heroic,
   hootenanny, hum, humming, hymnal, intonation, jam session, joyful,
   joyous, laughing, leaping, liturgical, lyric, lyricism,
   music festival, musicale, opera festival, operatic,
   operatic singing, psalmic, psalmodial, psalmodic, purring, radiant,
   rock festival, sacred, scat, scat singing, service of song, sing,
   sing-in, singfest, smiling, smirking, sol-fa, sol-fa exercise,
   solfeggio, solmization, song, soprano, sparkling, starry-eyed,
   swan song, tenor, thrice happy, tonic sol-fa, treble, vocal,
   vocal music, vocalization, warbling, yodel, yodeling