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]