Source : Webster's Revised Unabridged Dictionary (1913)

Intrusive \In*tru"sive\, a.
   Apt to intrude; characterized by intrusion; entering without
   right or welcome.

   {Intrusive rocks} (Geol.), rocks which have been forced,
      while in a plastic or melted state, into the cavities or
      between the cracks or layers of other rocks. The term is
      sometimes used as equivalent to plutonic rocks. It is then
      contrasted with effusive or volcanic rocks.

Source : WordNet®

intrusive
     adj 1: tending to intrude (especially upon privacy); "she felt her
            presence there was intrusive" [ant: {unintrusive}]
     2: of rock material; forced while molten into cracks between
        layers of other rock [ant: {extrusive}]
     3: thrusting inward; "an intrusive arm of the sea" [ant: {protrusive}]