The Collaborative International Dictionary of English v.0.48:

Vapid \Vap"id\ (v[a^]p"[i^]d), a. [L. vapidus having lost its
   life and spirit, vapid; akin to vappa vapid wine, vapor
   vapor. See Vapor.]
   Having lost its life and spirit; dead; spiritless; insipid;
   flat; dull; unanimated; as, vapid beer; a vapid speech; a
   vapid state of the blood.
   [1913 Webster]

         A cheap, bloodless reformation, a guiltless liberty,
         appear flat and vapid to their taste.    --Burke.
   [1913 Webster] -- Vap"id*ly, adv. -- Vap"id*ness, n.
   [1913 Webster]

WordNet (r) 3.0 (2006):

vapid
    adj 1: lacking taste or flavor or tang; "a bland diet"; "insipid
           hospital food"; "flavorless supermarket tomatoes"; "vapid
           beer"; "vapid tea" [syn: bland, flat, flavorless,
           flavourless, insipid, savorless, savourless,
           vapid]
    2: lacking significance or liveliness or spirit or zest; "a
       vapid conversation"; "a vapid smile"; "a bunch of vapid
       schoolgirls"

Moby Thesaurus II by Grady Ward, 1.0:

162 Moby Thesaurus words for "vapid":
   airy, arid, asinine, barren, betwixt and between, blah, bland,
   blank, bloodless, boring, catchpenny, changeable, characterless,
   cold, colorless, common, commonplace, dead, dilute, diluted,
   dismal, draggy, drearisome, dreary, driveling, dry, dryasdust,
   dull, dusty, effete, elephantine, empty, empty-headed,
   empty-minded, empty-pated, empty-skulled, etiolated, fade, fair,
   fair to middling, fairish, fatuous, flat, flavorless, flimsy,
   foolish, fribble, fribbling, frivolous, frothy, futile, gruelly,
   halfhearted, heavy, ho-hum, hollow, humdrum, idle, inane,
   indecisive, indifferent, inexcitable, infirm of purpose,
   infirm of will, innocuous, insipid, irresolute, jejune, lackluster,
   leaden, lifeless, light, low-spirited, matter-of-fact, mediocre,
   medium, middling, mild, milk-and-water, milky, moderate, modest,
   mundane, mushy, namby-pamby, neutral, nugacious, nugatory,
   of a kind, of a sort, of sorts, ordinary, otiose, pale, pallid,
   pappy, passable, pedestrian, plain, plodding, poetryless,
   pointless, poky, ponderous, prosaic, prosing, prosy, pulpy,
   rattlebrained, rattleheaded, respectable, sapless, savorless,
   scatterbrained, shallow, silly, slender, slight, slow, so-so,
   solemn, spiceless, spiritless, stale, sterile, stiff, stodgy,
   stuffy, superficial, tame, tasteless, tedious, thin, tiresome,
   tolerable, trifling, trite, trivial, unembellished, unflavored,
   unidealistic, unimaginative, unimpassioned, uninteresting,
   unlively, unpalatable, unpoetic, unromantic, unsavory, vacant,
   vacuous, vain, washy, watered, watered-down, watery, weak,
   wearisome, wearying, windy, wishy-washy, wooden