/ Dictionary / Index M mastoid: Meaning and Definition of Find definitions for: mas•toid Pronunciation: (mas'toid), [key] — adj. Anat. of or pertaining to the mastoid process. resembling a breast or nipple. —n. the mastoid process. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: mastoid (Thesaurus) mastodon mastoidectomy Related Content Daily Word Quiz: panacea Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language