a combining form meaning “outer,” “outside,” “external,” used in the formation of compound words: ectoderm.
Also especially before a vowel, ect-.
Origin of ecto-
combining form of Greek ektós outside
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
indicating outer, outside, externalectoplasm
Word Origin for ecto-
from Greek ektos outside, from ek, ex out
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-forming element generally meaning "outside, external," before vowels ect-, comb. form of Greek ektos "outside" (adv.), used to form scientific compounds in Greek; related to Greek ek, ex "out," from PIE *eghs- (see ex-).
Online Etymology Dictionary, © 2010 Douglas Harper
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.