As a Noun:
1. Behaviour which is foolish, silly or strange. English = foolishness, idiocy, craziness, stupidity.
2. A person whose behaviour is foolish, silly or strange. English = fool, idiot, madman. Informal English = loony.
3. Something written or said that you think is untrue, foolish or stupid. English = nonsense.
As a Verb or Adjective:
1. To say or do things which are foolish, silly or strange. English = (be) mad, (be) stupid, (be) crazy, (be) idiotic. Informal English = (be) loony.
2. To fool or take advantage of someone.
1. Used alone to mean that you think what someone has said is untrue, stupid or foolish. English = 'Nonsense!', 'Rubbish!'