a combining form meaning “within,” used in the formation of compound words: endocardial.
Also especially before a vowel, end-.

Origin of endo-

< Greek, combining form of éndon within; cognate with Old Irish ind-, OL endo- in, on
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2020

British Dictionary definitions for endo-


before a vowel end-

combining form

inside; withinendocrine

Word Origin for endo-

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

Medical definitions for endo-



Inside; within:endometrium.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.

Scientific definitions for endo-


A prefix meaning “inside,” as in endoskeleton.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.