Also ex-.

Origin of exo-

< Greek, combining form of éxō outside
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British Dictionary definitions for exo-


combining form
  1. external, outside, or beyondexobiology; exothermal

Word Origin for exo-

from Greek exō outside
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

Word Origin and History for exo-

word-forming element used in scientific words (e.g. exoskeleton), from Greek exo "outside," related to ex "out of" (see ex-).

Online Etymology Dictionary, © 2010 Douglas Harper

exo- in Medicine


  1. Outside; external:exoskeleton.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.

exo- in Science


  1. A prefix that means “outside” or “external,” as in exoskeleton.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.