noun
A somewhat literary or formal term for a foolish person; less common in casual speech than 馬鹿.
彼は自分のことを愚者だと言った。
He called himself a fool.
noun
The Fool (Tarot card)
Refers specifically to the Tarot card; used in fortune-telling contexts.
タロットカードの愚者は新しい旅立ちを表す。
The Fool tarot card represents a new beginning.
馬鹿 is the common, everyday word for 'fool' or 'idiot', while 愚者 is more literary and less insulting.
Compound of 愚 (foolish) and 者 (person). The exact historical derivation is uncertain, but the spelling is conventionally associated with the meaning 'foolish person'.