The Collaborative International Dictionary of English v.0.48:

Impertinent \Im*per"ti*nent\, a. [F., fr. L. impertinens,
   -entis; pref. im- not + pertinens. See Pertinent.]
   1. Not pertinent; not pertaining to the matter in hand;
      having no bearing on the subject; not to the point;
      irrelevant; inapplicable.
      [1913 Webster]

            Things that are impertinent to us.    --Tillotson.
      [1913 Webster]

            How impertinent that grief was which served no end!
                                                  --Jer. Taylor.
      [1913 Webster]

   2. Contrary to, or offending against, the rules of propriety
      or good breeding; guilty of, or prone to, rude,
      unbecoming, or uncivil words or actions; as, an impertient
      coxcomb; an impertient remark.
      [1913 Webster]

   3. Trifing; inattentive; frivolous.

   Syn: Rude; officious; intrusive; saucy; unmannerly;
        meddlesome; disrespectful; impudent; insolent.

   Usage: Impertinent, Officious, Rude. A person is
          officious who obtrudes his offices or assistance where
          they are not needed; he is impertinent when he
          intermeddles in things with which he has no concern.
          The former shows a lack of tact, the latter a lack of
          breeding, or, more commonly, a spirit of sheer
          impudence. A person is rude when he violates the
          proprieties of social life either from ignorance or
          wantonness. "An impertinent man will ask questions for
          the mere gratification of curiosity; a rude man will
          burst into the room of another, or push against his
          person, inviolant of all decorum; one who is officious
          is quite as unfortunate as he is troublesome; when he
          strives to serve, he has the misfortune to annoy."
          --Crabb. See Impudence, and Insolent.
          [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Impertinent \Im*per"ti*nent\, n.
   An impertinent person. [R.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

impertinent
    adj 1: characterized by a lightly pert and exuberant quality; "a
           certain irreverent gaiety and ease of manner" [syn:
           impertinent, irreverent, pert, saucy]
    2: not pertinent to the matter under consideration; "an issue
       extraneous to the debate"; "the price was immaterial";
       "mentioned several impertinent facts before finally coming to
       the point" [syn: extraneous, immaterial, impertinent,
       orthogonal]
    3: improperly forward or bold; "don't be fresh with me";
       "impertinent of a child to lecture a grownup"; "an impudent
       boy given to insulting strangers"; "Don't get wise with me!"
       [syn: fresh, impertinent, impudent, overbold,
       smart, saucy, sassy, wise]