noun-modifying (irregular)
Prenominal adjective describing something as laughably unreasonable or stupid. Often used to dismiss an idea, statement, or situation.
そんな馬鹿げた話は信じられない。
I can't believe such an absurd story.
彼の提案はまったく馬鹿げている。
His proposal is completely ridiculous.
馬鹿 is a noun/adjective meaning 'fool' or 'stupid', while 馬鹿げた is a prenominal adjective meaning 'absurd' or 'foolish' and is used attributively.
馬鹿らしい is an i-adjective meaning 'absurd' or 'ridiculous' and can be used predicatively, whereas 馬鹿げた is a prenominal adjective that only modifies nouns.
Derived from 馬鹿 (fool) + げ (suffix indicating appearance or state) + た (past/perfective attributive form), literally 'fool-like'. The exact historical derivation is uncertain, but it functions as a fixed prenominal adjective.