The Collaborative International Dictionary of English v.0.48:

Indiscreet \In`dis*creet"\, a. [OE. indiscret, F. indiscret, fr.
   L. indiscretus unseparated, indiscreet. See In- not, and
   Discreet, and cf. Indiscrete.]
   Not discreet; wanting in discretion.
   [1913 Webster]

         So drunken, and so indiscreet an officer. --Shak.

   Syn: Imprudent; injudicious; inconsiderate; rash; hasty;
        incautious; heedless; undiscerning; foolish. --
        In`dis*creet"ly, adv. -- In`dis*creet"ness, n.
        [1913 Webster]

WordNet (r) 3.0 (2006):

indiscreet
    adj 1: lacking discretion; injudicious; "her behavior was
           indiscreet at the very best" [ant: discreet]

Moby Thesaurus II by Grady Ward, 1.0:

97 Moby Thesaurus words for "indiscreet":
   audacious, blanket, bold, brash, brazen, brazenfaced, careless,
   casual, foolhardy, foolish, general, hasty, heedless, hubristic,
   ill-advised, ill-considered, ill-contrived, ill-devised,
   ill-gauged, ill-judged, impetuous, impolitic, improper,
   improvident, imprudent, impudent, impulsive, inadvisable,
   inappropriate, incautious, inconsiderate, indecent, indecorous,
   indelicate, indiscriminate, indiscriminative, inelegant,
   inexpedient, injudicious, insensate, insensitive, insolent,
   irrational, mindless, misadvised, misguided, myopic, naive,
   nonjudgmental, overbold, overcareless, overconfident, oversure,
   overweening, promiscuous, rash, reasonless, reckless, senseless,
   shortsighted, tactless, temerarious, thoughtless, unadvised,
   unbecoming, unchary, unconsidered, uncritical, uncriticizing,
   undemanding, undifferentiating, undiplomatic, undiscerning,
   undiscreet, undiscriminating, undiscriminative, unexacting,
   unfastidious, unforeseeing, unmeticulous, unparticular,
   unreasonable, unreflecting, unreflective, unseeing, unseemly,
   unselective, unsensible, unsound, unsubtle, untactful, unthinking,
   unthoughtful, unwary, unwise, wholesale, witless