The Collaborative International Dictionary of English v.0.48:

Tactless \Tact"less\, a.
   Destitute of tact.
   [1913 Webster]

WordNet (r) 3.0 (2006):

tactless
    adj 1: lacking or showing a lack of what is fitting and
           considerate in dealing with others; "in the circumstances
           it was tactless to ask her age" [syn: tactless,
           untactful] [ant: tactful]
    2: revealing lack of perceptiveness or judgment or finesse; "an
       inept remark"; "it was tactless to bring up those
       disagreeable" [syn: inept, tactless]

Moby Thesaurus II by Grady Ward, 1.0:

95 Moby Thesaurus words for "tactless":
   abrupt, airy, awkward, blanket, bluff, blunt, boorish, brash,
   brusque, bungling, caddish, careless, casual, clumsy, coarse,
   crude, cursory, degage, discourteous, disregardant, disregardful,
   disrespectful, easygoing, flippant, forgetful, free and easy,
   gauche, general, gruff, heedless, ill-bred, impertinent, impolite,
   impolitic, imprudent, inconsiderate, indelicate, indifferent,
   indiscreet, indiscriminate, indiscriminative, inept, injudicious,
   insensitive, insouciant, lazy, loutish, louty, maladroit, nasty,
   nonjudgmental, oblivious, offensive, offhand, perfunctory,
   promiscuous, reckless, regardless, respectless, rough, rude,
   thoughtless, uncivil, uncivilized, uncouth, uncritical,
   uncriticizing, undemanding, undifferentiating, undiplomatic,
   undiscreet, undiscriminating, undiscriminative, unexacting,
   unfastidious, unfeminine, ungenteel, ungentle, ungentlemanly,
   unheedful, unheeding, unladylike, unmeticulous, unmindful,
   unparticular, unrefined, unselective, unsolicitous,
   unsophisticated, unsubtle, untactful, unthinking, unwise, vulgar,
   wholesale