The Collaborative International Dictionary of English v.0.48:

Imprudence \Im*pru"dence\, n. [L. imprudentia: cf. F.
   imprudence. Cf. Improvidence.]
   The quality or state of being imprudent; want to caution,
   circumspection, or a due regard to consequences;
   indiscretion; inconsideration; rashness; also, an imprudent
   act; as, he was guilty of an imprudence.
   [1913 Webster]

         His serenity was interrupted, perhaps, by his own
         imprudence.                              --Mickle.
   [1913 Webster]

WordNet (r) 3.0 (2006):

imprudence
    n 1: a lack of caution in practical affairs [ant: prudence]

Moby Thesaurus II by Grady Ward, 1.0:

78 Moby Thesaurus words for "imprudence":
   absurdity, act of folly, blunder, brashness, brass,
   brazen boldness, callowness, casualness, cheek, childishness,
   chutzpah, crudity of intellect, dumb trick, folly, gall, heroics,
   hubris, immaturity, improvidence, impudence, inadvisability,
   inattention, inconsideration, indiscreetness, indiscretion,
   indiscriminateness, indiscrimination, inexpedience,
   injudiciousness, insensibility, insensitivity, insolence,
   irrationality, lack of feeling, lack of refinement, overboldness,
   overcarelessness, overconfidence, oversureness, overweeningness,
   pompousness, promiscuity, promiscuousness, puerility, rashness,
   reasonlessness, recklessness, senselessness, sottise, stuffiness,
   stupid thing, stupidity, syncretism, tactlessness, temerariousness,
   temerity, thoughtlessness, unchariness, uncriticalness,
   undiscriminatingness, undiscriminativeness, unfastidiousness,
   unintelligence, unmeticulousness, unparticularness, unpreciseness,
   unreason, unreasonableness, unselectiveness, unsensibleness,
   unsoundness, untactfulness, unthoughtfulness, unwariness, unwisdom,
   unwise step, unwiseness, witlessness