The Collaborative International Dictionary of English v.0.48:

Extrusion \Ex*tru"sion\, n.
   The act of thrusting or pushing out; a driving out;
   expulsion.
   [1913 Webster]

WordNet (r) 3.0 (2006):

extrusion
    n 1: something that bulges out or is protuberant or projects
         from its surroundings; "the gun in his pocket made an
         obvious bulge"; "the hump of a camel"; "he stood on the
         rocky prominence"; "the occipital protuberance was well
         developed"; "the bony excrescence between its horns" [syn:
         bulge, bump, hump, swelling, gibbosity,
         gibbousness, jut, prominence, protuberance,
         protrusion, extrusion, excrescence]
    2: squeezing out by applying pressure; "an unexpected extrusion
       of toothpaste from the bottom of the tube"; "the expulsion of
       pus from the pimple" [syn: extrusion, expulsion]

Moby Thesaurus II by Grady Ward, 1.0:

58 Moby Thesaurus words for "extrusion":
   bas-relief, bellying, boldness, booting out, bulging,
   defenestration, detrusion, discharge, effusion, egestion,
   ejaculation, ejection, ejectment, elimination, emanation,
   embossment, emergence, emersion, eminence, emission, excrescence,
   excrescency, excretion, expulsion, extravasation, exudation, flow,
   flux, gibbosity, gibbousness, high relief, issuance, issue,
   jettison, kicking downstairs, low relief, obtrusion, ouster,
   ousting, projection, prominence, protrusion, protuberance,
   protuberancy, rejection, relief, removal, salience, salient,
   secretion, surfacing, the boot, the bounce, throwing out,
   transudation, tuberosity, tuberousness, vent