The Collaborative International Dictionary of English v.0.48:

Whirligig \Whirl"i*gig\, n. [Whirl + gig.]
   [1913 Webster]
   1. A child's toy, spun or whirled around like a wheel upon an
      axis, or like a top. --Johnson.
      [1913 Webster]

   2. Anything which whirls around, or in which persons or
      things are whirled about, as a frame with seats or wooden
      horses.
      [1913 Webster]

            With a whirligig of jubilant mosquitoes spinning
            about each head.                      --G. W. Cable.
      [1913 Webster]

   3. A mediaeval instrument for punishing petty offenders,
      being a kind of wooden cage turning on a pivot, in which
      the offender was whirled round with great velocity.
      [1913 Webster]

   4. (Zool.) Any one of numerous species of beetles belonging
      to Gyrinus and allied genera. The body is firm, oval or
      boatlike in form, and usually dark colored with a
      bronzelike luster. These beetles live mostly on the
      surface of water, and move about with great celerity in a
      gyrating, or circular, manner, but they are also able to
      dive and swim rapidly. The larva is aquatic. Called also
      weaver, whirlwig, and whirlwig beetle.
      [1913 Webster]

WordNet (r) 3.0 (2006):

whirligig
    n 1: a conical child's plaything tapering to a steel point on
         which it can be made to spin; "he got a bright red top and
         string for his birthday" [syn: top, whirligig,
         teetotum, spinning top]
    2: a large, rotating machine with seats for children to ride or
       amusement [syn: carousel, carrousel, merry-go-round,
       roundabout, whirligig]
    v 1: whirl or spin like a whirligig

Moby Thesaurus II by Grady Ward, 1.0:

42 Moby Thesaurus words for "whirligig":
   April showers, Ferris wheel, Proteus, carousel, chameleon,
   chute-the-chutes, chutes, cloud shapes, disk, flying horses,
   gyrate, gyre, kaleidoscope, mercury, merry-go-round, moon,
   pirouette, purl, quicksilver, roller, roller coaster,
   rolling stone, rotator, rotor, roundabout, rundle, seesaw,
   shifting sands, swing, teeter-totter, the weather, top, twirl,
   water, weather vane, weathercock, wheel, wheel of fortune, whip,
   whirl, whirlabout, whirler