Unexpected; not anticipated — used to describe something that was unforeseen or surprising.
思わぬ知らせに、彼は言葉を失った。
He was at a loss for words at the unexpected news.
思わぬ出費があって、貯金が減ってしまった。
An unforeseen expense came up and my savings went down.
思わぬ人がパーティーに来て、みんな驚いた。
An unexpected person came to the party and everyone was surprised.