The Collaborative International Dictionary of English v.0.48:

Insipid \In*sip"id\, a. [L. insipidus; pref. in- not + sapidus
   savory, fr. sapere to taste: cf. F. insipide. See Savor.]
   [1913 Webster]
   1. Wanting in the qualities which affect the organs of taste;
      without taste or savor; vapid; tasteless; as, insipid
      drink or food. --Boyle.
      [1913 Webster]

   2. Wanting in spirit, life, or animation; uninteresting;
      weak; vapid; flat; dull; heavy; as, an insipid woman; an
      insipid composition.
      [1913 Webster]

            Flat, insipid, and ridiculous stuff to him. --South.
      [1913 Webster]

            But his wit is faint, and his salt, if I may dare to
            say so, almost insipid.               --Dryden.

   Syn: Tasteless; vapid; dull; spiritless; unanimated;
        lifeless; flat; stale; pointless; uninteresting.
        Insipidity

WordNet (r) 3.0 (2006):

insipid
    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 interest or significance or impact; "an insipid
       personality"; "jejune novel" [syn: insipid, jejune]

Moby Thesaurus II by Grady Ward, 1.0:

152 Moby Thesaurus words for "insipid":
   arid, banal, bare, barren, betwixt and between, blah, bland, blank,
   bleached, bloodless, bromidic, changeable, characterless, clear,
   cold, colorless, common, commonplace, dead, devoid, dilute,
   diluted, dismal, distasteful, draggy, drearisome, dreary,
   driveling, dry, dryasdust, dull, dusty, effete, elephantine, empty,
   etiolated, fade, fair, fair to middling, fairish, featureless,
   feeble, flat, flavorless, gruelly, halfhearted, heavy, ho-hum,
   hollow, humdrum, ill-flavored, inane, indecisive, indifferent,
   inexcitable, infirm of purpose, infirm of will, innocuous,
   irresolute, jejune, lackluster, leaden, lifeless, low-spirited,
   matter-of-fact, mediocre, medium, middling, mild, milk-and-water,
   milky, moderate, modest, mundane, mushy, namby-pamby, neutral,
   null, null and void, of a kind, of a sort, of sorts, ordinary,
   pale, pallid, pappy, passable, pedestrian, plain, plodding,
   poetryless, pointless, poky, ponderous, prosaic, prosing, prosy,
   pulpy, respectable, sapless, savorless, slight, slow, so-so, soft,
   solemn, spiceless, spiritless, stale, sterile, stiff, stodgy,
   stuffy, subdued, superficial, swashy, tame, tasteless, tedious,
   tenuous, thin, tiresome, tolerable, unappetizing, unembellished,
   unflavored, unidealistic, unimaginative, unimpassioned,
   uninteresting, unlively, unpoetic, unrelieved, unromantic,
   unsavory, vacant, vacuous, vapid, void, washy, watered,
   watered-down, waterish, watery, weak, weariful, wearisome, white,
   wishy-washy, with nothing inside, without content, wooden