na-adjective, adverb taking the 'to' particle, noun
Describes something contrary to what one thought or assumed. Often used as 意外に or 意外と (adverbially) meaning 'unexpectedly' or 'more/less than expected'. Can also be used as a na-adjective or noun.
彼が試験に落ちたのは意外だった。
It was surprising that he failed the exam.
この料
This dish is unexpectedly delicious.
意外なことに、彼女はもう結婚していた。
Surprisingly, she was already married.