Synonyms for Insane:

adj.

chaotic (adjective)
frenzied, disorganized, inexact, blurry, cluttered, chaotic, indefinite, jumbled, embroiled, disarrayed, out of control, undisciplined, lawless, tempestuous, deranged, shapeless, inchoate, lax, perturbed, Disintegrated, disconnected, fuzzy, confused, amorphous, inconsistent, indistinct, muddled, obscure, messy, anarchistic, unruly, uneven, discomposed, disheveled, anarchical, frantic, rambunctious, tumultuous, wild, disorderly, irregular, formless, loose, incoherent, disordered, deformed.
crazed (adjective)
berserk.
deranged (adjective)
nutty.
foolish (adjective)
zany, loopy, dippy, imbecilic, tomfool.
haywire (adjective)
haywire, amok.
insane (adjective)
feverish, kooky, psychotic, blithering, berserk, frenzied, irrational, crazy, psycho, babbling, Crack-brained, brain-sick, nutty, mad, schizoid, neurotic, demented, unbalanced, delirious, deranged, hysterical, maniacal, batty, lunatic.
lunatic (adjective)
schizoid.
mentally ill; foolish (adjective)
idiotic, crazed, psychotic, irrational, maniacal, psychopathic, cracked, loony, preposterous, nutty, of unsound mind, unhinged, nuts, paranoid, crazy, deranged, raging, lunatic, schizophrenic, moonstruck, batty, unsettled, cuckoo, wild, mad, touched, demented, raving, rabid, daft, frenzied, screwy.
softheaded (adjective)
softheaded.
touched (adjective)
pixilated.

n.

ludicrous, ridiculous, laughable, childish, over-the-top, not in your right mind/not right in the head. madcap. jerky, cockeyed, absurd, imbecilic, silly, nonsensical, softheaded, preposterous, zany, tomfool, sappy, knowledge, unearthly, ability, dippy, moronic, dopey. deranged (noun)
crazy, unbalanced, nutty, bonkers, bats, touched, lunatic, cuckoo, batty, balmy, screwy, round the bend, demented, crazed, mad, nuts, loco, loony, psychotic, bananas, unhinged, cracked.
insane (noun)
mad, lunatic, daft, batty, psychopathological, noncompos mentis, unsound, unhinged, around the bend, balmy, possessed, disturbed, maniac, non compos mentis, raving, dotty, kookie, bats, crackers, manic-depressive, brainsick, certifiable, berserk, loony, of unsound mind, loopy, round the bend, psychopathologic, raving mad, screw-loose, crazy, kooky, cracked, crackbrained, foolish, demoniac, screwy, idiotic, paranoid, unbalanced, nutty, wacky, maniacal, fruity, bonkers, sick, unstable, barmy, moonstruck, wild, demoniacal, half-crazed, hebephrenic, distracted, nuts, maniclike, harebrained, psychopathic, crazed, schizophrenic, haywire, mentally ill, amok, deranged, whacky, certified, psychotic, fey, loco, demented, buggy, amuck, touched.
mentally ill (noun)
diminished responsibility, bipolar, depressed.

Other synonyms:

jerky, dippy, bananas, ridiculous, madcap, over-the-top, softheaded, ludicrous, laughable, Daffy. distraught, preposterous, cockeyed, absurd, moronic, nonsensical, imbecilic, gaga. childish, sappy, zany, dopey, silly. unearthly. wrong. crazy
off.
mentally ill
diminished responsibility, bipolar, mentally ill, depressed.
Other relevant words:
dopey, certifiable, rabid, raving mad, softheaded, ridiculous, laughable, haywire, violent, half-crazed, dotty, cuckoo, raving, amok, screw-loose, loony, certified, wrong, fey, balmy, demoniac, off, of unsound mind, brainsick, screwy, psychopathological, crackbrained, demoniacal, mentally ill, distraught, buggy, foolish, non compos mentis, gaga, unsound, crazed, around the bend, touched, unearthly, moonstruck, sick, harebrained, possessed, madcap, ludicrous, cockeyed, paranoid, fruity, nuts, maniac, depressed, zany, absurd, amuck, wacky, whacky, hebephrenic, Deluded, distracted, jerky, silly, unsettled, kookie, schizophrenic, dippy, moronic, barmy, loco, loopy, preposterous, daft, over-the-top, crackers, cracked, bats, bananas, unhinged, tomfool, manic-depressive, round the bend, psychopathologic, maniclike, bipolar, imbecilic, Daffy, raging, disturbed, unstable, psychopathic, idiotic, sappy, nonsensical, bonkers, childish.

Usage examples for insane

  1. The fellow belongs in an insane asylum. – The Future Belongs to the People by Karl Liebknecht
  2. While Alexander of Parma, sorely against his will and in obedience to what, he deemed the insane suggestions of his master, was turning his back on the Netherlands in order to relieve Paris, now hard pressed by the Bearnese, an opportunity offered itself of making at least a beginning in the great enterprise of recovering these most valuable possessions. – Project Gutenberg History of The Netherlands, 1555-1623, Complete by John Lothrop Motley