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a combining form meaning “breast,” used in the formation of compound words: mastopathy.
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Which of the following nouns has an irregular plural form?
Also especially before a vowel, mast-.

Origin of masto-

Combining form representing Greek mastós breast
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2022


What does masto- mean?

Masto- is a combining form used like a prefix meaning “breast.” It is often used in medical terms, especially in anatomy and pathology.

Masto- comes from the Greek mastós, meaning “breast.” The Latin-based analog to masto- is mammo-, from mamma, meaning “breast.”

What are variants of masto-?

When combined with words or word elements that begin with a vowel, masto- becomes mast-, as in mastectomy.

Examples of masto-

One example of a medical term that features the combining form masto- is mastotomy, also known as a mammotomy, meaning “incision of the breast.”

We know that masto- means “breast.” The -tomy part of the word may also look familiar; it is a combining form meaning “incision.” Mastotomy literally translates to “breast incision.”

What are some words that use the combining form masto-?

What are some other forms that masto- may be commonly confused with?

While it doesn’t use the combining form masto-, mastodon, an extinct elephant-like animal, also comes from the same Greek word for “breast.” Learn more about where the word mastodon comes from at our entry for the word.

Also note that mast cells, from the German Mast (“fattening of animals for slaughter”), are not related to masto-. These cells give their name to such conditions as mastocytosis.

Break it down!

The combining form pathy has various meanings, including “disease.” With this in mind, what does mastopathy mean in everyday language?

How to use masto- in a sentence

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

Medical 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.