Literary or formal term for ignorance and foolishness. Rare in everyday speech; more common synonyms are 愚か (おろか) or 馬鹿 (ばか).
Everyone was appalled by his foolish behavior.
It was a remark that exposed his ignorance.
Compound of 愚 (ぐ, 'foolish') and 蒙 (もう, 'ignorant'). The exact historical derivation is uncertain; the spelling is conventionally associated with the meaning of ignorance and stupidity.