1 [more insane; most insane] : not sane: such as a : having or showing severe mental illness
Usage The use of insane to describe a person with severe mental illness is now often considered offensive. The phrase mentally ill is preferred. Insane in this sense now occurs chiefly in such legal phrases as criminally insane and temporarily insane. b : unable to think in a clear or sensible way c — used in the phrase drive/make (someone) insane to describe annoying or bothering someone very much.