The Collaborative International Dictionary of English v.0.48:

Intrude \In*trude"\, v. i. [L. intrudere, intrusum; pref. in- in
   + trudere to thrust, akin to E. threat. See Threat.]
   To thrust one's self in; to come or go in without invitation,
   permission, or welcome; to encroach; to trespass; as, to
   intrude on families at unseasonable hours; to intrude on the
   lands of another.
   [1913 Webster]

         Thy wit wants edge
         And manners, to intrude where I am graced. --Shak.
   [1913 Webster]

         Some thoughts rise and intrude upon us, while we shun
         them; others fly from us, when we would hold them. --I.
                                                  Watts.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Intrude \In*trude"\, v. t. [imp. & p. p. Intruded; p. pr. &
   vb. n. Intruding.]
   [1913 Webster]
   1. To thrust or force (something) in or upon; especially, to
      force (one's self) in without leave or welcome; as, to
      intrude one's presence into a conference; to intrude one's
      opinions upon another.
      [1913 Webster]

   2. To enter by force; to invade. [Obs.]
      [1913 Webster]

            Why should the worm intrude the maiden bud? --Shak.
      [1913 Webster]

   3. (Geol.) The cause to enter or force a way, as into the
      crevices of rocks.

   Syn: To obtrude; encroach; infringe; intrench; trespass. See
        Obtrude.
        [1913 Webster]

WordNet (r) 3.0 (2006):

intrude
    v 1: enter uninvited; "They intruded on our dinner party"; "She
         irrupted into our sitting room" [syn: intrude, irrupt]
    2: enter unlawfully on someone's property; "Don't trespass on my
       land!" [syn: trespass, intrude]
    3: search or inquire in a meddlesome way; "This guy is always
       nosing around the office" [syn: intrude, horn in, pry,
       nose, poke]
    4: thrust oneself in as if by force; "The colors don't intrude
       on the viewer" [syn: intrude, obtrude]

Moby Thesaurus II by Grady Ward, 1.0:

120 Moby Thesaurus words for "intrude":
   admit, advance upon, barge in, be admitted, blow it, bother,
   break bounds, break in, break in upon, breeze in, burst in,
   bust in, butt in, charge in, come barging in, come between,
   come breezing in, come busting in, come in, crash, crash in,
   crash the gates, creep in, cross the threshold, crowd in, cut in,
   disturb, drag in, drop in, edge in, elbow in, encroach, enter,
   entrench, foist in, fudge in, gain admittance, get in, go in,
   go into, go off half-cocked, go too far, have an entree,
   have an in, hop in, horn in, impinge, implant in, impose,
   impose on, impose upon, infiltrate, infringe, inject in, insert,
   insert in, insinuate, insinuate in, intercalate, interfere,
   interjaculate, interject, interlope, intermeddle, interpolate,
   interpose, interrupt, intervene, introduce, introduce in, invade,
   irrupt, jam in, jump in, know no bounds, look in, lug in,
   make an inroad, meddle, muscle, obtrude, overstep,
   overstep the bounds, pack in, pester, pop in, press in, presume,
   push in, put between, put in, put on, put upon, run in, rush in,
   sandwich, set foot in, slink in, slip in, smash in, smuggle in,
   sneak in, speak inopportunely, speak too late, squeeze in,
   steal in, step in, storm in, take in, throng in, throw in,
   thrust in, transgress, trench, trespass, usurp, visit, wedge in,
   work in, worm in