a combining form meaning “breast,” used in the formation of compound words: mastopathy.
Also especially before a vowel, mast-.

Origin of masto-

combining form representing Greek mastós breast Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

British Dictionary definitions for masto-


before a vowel mast-

combining form

indicating the breast, mammary glands, or something resembling a breast or nipplemastodon; mastoid

Word Origin for masto-

from Greek mastos breast
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

Medicine definitions for masto-



Breast; mammary gland; nipple:mastectomy.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.