A prenominal adjective meaning unexpected or unlikely (used before nouns, e.g., 'an unexpected disaster').
とんだ勘違いで、二重予約になってしまった。
Because of an unexpected misunderstanding, there was a double booking.
とんだ災難に見舞われた家族を支援した。
We supported the family struck by an unforeseen disaster.
彼の一言でとんだ騒ぎが起きた。
His single remark caused an unexpected commotion.
A prenominal adjective meaning terrible, awful, or outrageous (e.g., 'a terrible insult').
そんなことを言うなんて、とんだ失礼だ。
To say something like that is outrageous rudeness.
彼はとんだ嘘つきだとわかった。
It turned out he was a terrible liar.
An obsolete adverbial usage meaning extremely or very (rare in modern Japanese).
（古風）とんだ喜びに涙が止まらなかった。
(Arch.) I was so extremely delighted that I couldn't stop crying.