As a Noun:
1. The state of mind which causes someone to talk or behave in a very strange or foolish way. English = craziness, insanity, madness. Informal English = looniness.
As a Verb or Adjective:
1. To talk or behave in a very strange or foolish way. English = (be) crazy, (be) insane, (be) mad. Informal English = (be) loony, (be) loopy. Idiomatic English = (be) out of one's mind.