Roget's Thesaurus: Entry 320 (Levity)

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#320. Levity. -- N. levity; lightness &c. adj.; imponderability, buoyancy, volatility.

feather, dust, mote, down, thistle, down, flue, cobweb, gossamer, straw, cork, bubble, balloon; float, buoy; ether, air.

leaven, ferment, barm[obs], yeast.

lighter-than-air balloon, helium balloon, hydrogen balloon, hot air balloon.

convection, thermal draft, thermal.

V. be light &c. adj.; float, rise, swim, be buoyed up.

render light &c. adj.; lighten, leaven.

Adj. light, subtile, airy; imponderous[obs], imponderable; astatic[obs], weightless, ethereal, sublimated; gossamery; suberose[obs], suberous[obs]; uncompressed, volatile; buoyant, floating &c. v.; portable.

light as a feather, light as a thistle, light as air; lighter than air; rise like a balloon, float like a balloon