Source : Webster's Revised Unabridged Dictionary (1913)

Extrusive \Ex*tru"sive\, a. [See {Extrude}.] (Geol.)
   Forced out at the surface; as, extrusive rocks; -- contrasted
   with {intrusive}.

Source : WordNet®

extrusive
     adj : of rock material; forced out while molten through cracks in
           the earth's surface [ant: {intrusive}]