Mawson, C.O.S., ed. (1870–1938). Roget’s International Thesaurus. 1922.

Class III. Words Relating to Matter
Section I. Matter in General
4. Motion with Reference to Direction

320. Levity.

   NOUN:LEVITY; lightness &c. adj.; imponderability, buoyancy, volatility; imponderables [tech.].
  [COMPARISONS] feather, dust, mote, down, thistledown, flue, fluff, cobweb, gossamer, straw, cork, bubble; float, buoy; ether, air.
  FERMENT, leaven, barm, yeast, zyme, enzyme, pepsin, diastase.
   VERB:BE LIGHT &c. adj.; float, swim, be buoyed up.
  RENDER LIGHT &c. adj.; lighten.
  FERMENT, work, raise, leaven.
   ADJECTIVE:LIGHT, subtile, subtle, airy; imponderous, imponderable; astatic, weightless, ethereal, sublimated; gossamery; suberose or suberous, subereous; uncompressed, volatile; buoyant, floating &c. v.; foamy, frothy; portable.
  light as -a feather, – thistledown, – air.
  FERMENTING, fermentative, zymogenic, zymologic or zymological, diastatic, yeasty.
   QUOTATION:Trifles light as air.—Othello