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]

Moby Thesaurus II by Grady Ward, 1.0:

87 Moby Thesaurus words for "impertinent":
   adrift, arrogant, audacious, beside the mark, beside the point,
   beside the question, biggety, bluff, bold, brash, brassy, brazen,
   bumptious, busy, busybody, challenging, cheeky, chutzpadik, cocky,
   contemptuous, crusty, daring, defiant, defying, derisive,
   discourteous, disdainful, disregardful, disrespectful, extraneous,
   extrinsic, facy, flip, flippant, foreign, forward, fresh, gally,
   gratuitous, greatly daring, immaterial, impolite, impudent,
   inadmissible, inapplicable, inapposite, inappropriate, incidental,
   inconsequent, inquisitive, insolent, interfering, intrusive,
   irrelative, irrelevant, malapert, meddlesome, meddling, nervy,
   nihil ad rem, nonessential, nosy, not at issue, obtrusive,
   off the subject, offensive, officious, out-of-the-way,
   parenthetical, pert, presumptuous, prying, pushing, pushy,
   regardless of consequences, rude, sassy, saucy, self-appointed,
   smart, smart-alecky, smart-ass, snoopy, uncalled-for, uncivil,
   unessential, wise-ass



Bouvier's Law Dictionary, Revised 6th Ed (1856):

IMPERTINENT, practice, pleading. What does not appertain, or belong to; id
est, qui ad rem non pertinet.
     2. Evidence of facts which do not belong to the matter in question, is
impertinent and inadmissible. In general, what is immaterial is impertinent,
and what is material is, in general, not impertinent. 1 McC. & Y. 337. See
Gresl. Ev. Ch. 3, s. 1, p. 229. Impertinent matter, in a declaration or
other pleading is that which does not belong to the subject; in such case it
is considered as mere surplusage, (q.v.) and is rejected. Ham. N. P. 25.
Vide 2 Ves. 24; 5 Madd. R. 450; Newl. Pr. 38; 2 Ves. 631; 5 Ves. 656; 18
Eng. Com. Law R. 201; Eden on Inj. 71.
     3. There is a difference between matter merely impertinent and that
which is scandalous; matter may be impertinent, without being scandalous;
but if it is scandalous, it must be impertinent.
    4. In equity a bill cannot, according to the general practice, be
referred for impertinence after the defendant has answered or submitted to
answer, but it may be referred for scandal at any time, and even upon the
application of a stranger to the suit. Coop. Eq. Pl. 19; 2 Ves. 631; 6 Ves.
514; Story, Eq. Pl. Sec. 270. Vide Gresl. Eq. Ev. p. 2, c. 3, s, 1; 1 John.
Ch. R. 103; 1 Paige's R. 555; I Edw. R. 350; 11 Price, R. 111; 5 Paige's R.
522; 1 Russ. & My. 28; Bouv. Inst. Index, h.t.; Scandal.