agent, alterant, alterative, alterer, catalyst, catalytic agent, ferment, foam, froth, innovationist, innovator, introducer, lather, leaven, modificator, modifier, precursor, spume, suds, transformer, transmogrifier
levity, lightness, imponderability, buoyancy, volatility, feather, dust, mote, down, thistle, down, flue, cobweb, gossamer, straw, cork, bubble, balloon, float, buoy, ether, air, leaven, ferment, barm, yeast
, lighter-than-air balloon, helium balloon, hydrogen balloon, hot air balloon, convection, thermal draft, thermal, light, subtile, airy, imponderous, imponderable, astatic, weightless, ethereal, sublimated, gossamery, suberose, suberous, uncompressed, volatile, buoyant, floating, portable, light as a feather, light as a thistle, light as air, lighter than air, rise like a balloon, float like a balloon.
bubble; cloud, bubble, foam, froth, head, spume, lather, suds, spray, surf, yeast
, barm, spindrift, cloud, vapor, fog, mist, haze, steam, geyser, scud, messenger, rack, nimbus, cumulus, woolpack, cirrus, stratus, cirrostratus, cumulostratus, cirrocumulus, mackerel sky, mare's tale, dirty sky, curl cloud, frost smoke, thunderhead, nephelognosy, nephograph, nephology, effervescence, fermentation, bubbling, nebula, cloudliness, nebulosity, bubbling, frothy, nappy, effervescent, sparkling, mousseux, frothy, up, cloudy, thunderheaded, vaporous, nebulous, overcast, the lowring element scowls o'er the darkened lands.