noun
Refers to an outstanding work of art, literature, or craft; a classic or crowning achievement.
この小説は彼の最高傑作だ。
This novel is his greatest masterpiece.
あの映画はまさに傑作と言
That movie can truly be called a masterpiece.
na-adjective, noun
hilarious (unintentionally); absurd; outrageous
Jocular, dated usage: describes a blunder, remark, or situation so bad or absurd that it becomes funny. Often used with な, as in 傑作な話.
彼の失敗談は傑作だった。
His story of failure was unintentionally hilarious.
あの言い間違いは傑作だね。
That slip of the tongue is absurdly funny, isn't it?