The Collaborative International Dictionary of English v.0.48:

Imprudent \Im*pru"dent\, a. [L. imprudens; pref. im- not +
   prudens prudent: cf. F. imprudent. See Prudent, and cf.
   Improvident.]
   Not prudent; wanting in prudence or discretion; indiscreet;
   injudicious; not attentive to consequence; improper. --
   Im*pru"dent*ly, adv.
   [1913 Webster]

         Her majesty took a great dislike at the imprudent
         behavior of many of the ministers and readers.
                                                  --Strype.
   [1913 Webster]

   Syn: Indiscreet; injudicious; incautious; ill-advised;
        unwise; heedless; careless; rash; negligent.
        [1913 Webster]

WordNet (r) 3.0 (2006):

imprudent
    adj 1: not prudent or wise; "very imprudent of her mother to
           encourage her in such silly romantic ideas"; "would be
           imprudent for a noneconomist to talk about the details of
           economic policy"- A.M.Schlesinger [ant: prudent]
    2: lacking wise self-restraint; "an imprudent remark"