The Collaborative International Dictionary of English v.0.48:

Frothy \Froth"y\, a. [Compar. Frothier; superl. Frothiest.]
   1. Full of foam or froth, or consisting of froth or light
      bubbles; spumous; foamy.
      [1913 Webster]

   2. Not firm or solid; soft; unstable. --Bacon.
      [1913 Webster]

   3. Of the nature of froth; light; empty; unsubstantial; as, a
      frothy speaker or harangue. --Tillotson.
      [1913 Webster]

WordNet (r) 3.0 (2006):

frothy
    adj 1: emitting or filled with bubbles as from carbonation or
           fermentation; "bubbling champagne"; "foamy (or frothy)
           beer" [syn: bubbling, bubbly, foaming, foamy,
           frothy, effervescing, spumy]
    2: marked by high spirits or excitement; "his fertile
       effervescent mind"; "scintillating personality"; "a row of
       sparkly cheerleaders" [syn: bubbling, effervescent,
       frothy, scintillating, sparkly]

Moby Thesaurus II by Grady Ward, 1.0:

90 Moby Thesaurus words for "frothy":
   airy, asinine, barmy, birdbrained, birdwitted, brave, bravura,
   braw, bubbly, catchpenny, chichi, daring, dashing, downy, dressy,
   empty, ethereal, exhibitionistic, fatuous, featherbrained,
   feathery, flashing, flashy, flaunting, flighty, flimsy, fluffy,
   foam-flecked, foamy, foolish, fribble, fribbling, frilly,
   frivolous, futile, gallant, gay, glittering, gossamery, heady,
   idle, imponderous, inane, jaunty, jazzy, lathery, leger, light,
   light as air, lighter than vanity, mousse, nugacious, nugatory,
   otiose, rakish, shallow, shallow-headed, shallow-minded,
   shallow-pated, shallow-witted, showy, silly, slender, slight,
   snazzy, soapsuddy, soapsudsy, soapy, souffle, splashy, splurgy,
   sporty, spumose, spumous, spumy, suddy, sudsy, superficial,
   trifling, trite, trivial, unheavy, unprofound, vacuous, vain,
   vapid, volatile, weightless, windy, yeasty