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a combining form meaning “tumor,” “mass,” used in the formation of compound words:
Origin of onco-
combining form of Greek ónkos mass, bulk Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2018.
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British Dictionary definitions for onco-


combining form
denoting a tumour: oncology
Word Origin
from Greek onkos
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 onco-

word-forming element meaning "bulk, mass," especially in medical use, "tumor," from Latinized form of Greek onko-, comb. form of onkos "bulk, size, mass, body."

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

onco- pref.

  1. Tumor: oncology.

  2. Mass; swelling: oncolysis.

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