Synonyms for Foolishness (same or very similar meaning)
WordNet sense 1 (the quality of being rash and foolish):
craziness, folly, madnessWordNet sense 2 (the trait of acting stupidly or rashly):
unwisenessWordNet sense 3 (a stupid mistake):
imbecility, stupidity, betiseFrom the ODE community, based on WordNetadd/edit