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[in-troo-zhuh n] /ɪnˈtru ʒən/
an act or instance of intruding.
the state of being intruded.
  1. an illegal act of entering, seizing, or taking possession of another's property.
  2. a wrongful entry after the determination of a particular estate, made before the remainderman or reversioner has entered.
  1. emplacement of molten rock in preexisting rock.
  2. plutonic rock emplaced in this manner.
  3. a process analogous to magmatic intrusion, as the injection of a plug of salt into sedimentary rocks.
  4. the matter forced in.
Origin of intrusion
1250-1300; Middle English < Medieval Latin intrūsiōn- (stem of intrūsiō), equivalent to Latin intrūs(us), past participle of intrūdere to intrude (equivalent to intrūd- verb stem + -tus past participle suffix, with dt < s) + -iōn- -ion
Related forms
intrusional, adjective Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2018.
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British Dictionary definitions for intrusion


the act or an instance of intruding; an unwelcome visit, interjection, etc: an intrusion on one's privacy
  1. the movement of magma from within the earth's crust into spaces in the overlying strata to form igneous rock
  2. any igneous rock formed in this way
(property law) an unlawful entry onto land by a stranger after determination of a particular estate of freehold and before the remainderman or reversioner has made entry
Derived Forms
intrusional, adjective
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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Word Origin and History for intrusion

late 14c., from Old French intrusion (14c.), from Medieval Latin intrusionem (nominative intrusio) "a thrusting in," noun of action from past participle stem of Latin intrudere, from in- "in" (see in- (2)) + trudere "to thrust, push" (see extrusion).

Online Etymology Dictionary, © 2010 Douglas Harper
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intrusion in Science
The movement of magma through cracks in underground rocks within the Earth, usually in an upward direction. ◇ Rocks that form from the underground cooling of magma are generally coarse-grained (because they cool slowly so that large crystals have time to grow) and are called intrusive rocks. Compare extrusion.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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