masto-

masto-

or mast-

pref.

Breast; mammary gland; nipple: mastectomy.

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[From Greek mastos, breast.]

American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

masto-

or before a vowel

mast-

combining form

indicating the breast, mammary glands, or something resembling a breast or nipple: mastodon; mastoid.

[from Greek mastos breast]

Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014