/ Dictionary / Index A alienist: Meaning and Definition of Find definitions for: al•ien•ist Pronunciation: (āl"yu-nist, ā"lē-u-), [key] — n. (formerly) a doctor specializing in the treatment of mental illness. an expert witness in a sanity trial. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: alienist (Thesaurus) alienism alienor Related Content Daily Word Quiz: perspicacious Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language