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a combining form meaning “within,” used in the formation of compound words:
Also, especially before a vowel, end-.
Origin of endo-
< Greek, combining form of éndon within; cognate with Old Irish ind-, OL endo- in, on Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2018.
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British Dictionary definitions for endo-


combining form
inside; within: endocrine
Word Origin
from Greek, from endon within
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 endo-

word-forming element meaning "inside, within, internal," comb. form of Greek endon "in, within," literally "in the house of," from en "in" (see en- (2)) + base of domos "house" (see domestic).

Online Etymology Dictionary, © 2010 Douglas Harper
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endo- in Medicine

endo- or end-
Inside; within: endometrium.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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endo- in Science
A prefix meaning "inside," as in endoskeleton.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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