[ in-seyn ]
/ ɪnˈseɪn /


not sane; not of sound mind; mentally deranged.
of, relating to, or characteristic of a person who is mentally deranged: insane actions; an insane asylum.
utterly senseless: an insane plan.

Origin of insane

From the Latin word insānus, dating back to 1550–60. See in-3, sane

Related forms

in·sane·ly, adverbin·sane·ness, nounpseu·do·in·sane, adjective Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Examples from the Web for insane

British Dictionary definitions for insane


/ (ɪnˈseɪn) /


  1. mentally deranged; crazy; of unsound mind
  2. (as collective noun; preceded by the)the insane
characteristic of a person of unsound mindan insane stare
irresponsible; very foolish; stupid

Derived Forms

insanely, adverbinsaneness, noun
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 insane


[ ĭn-sān ]


Of, exhibiting, or afflicted with insanity.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.