Unexpected
Surprising
adverb, noun, な adjective
Something outside your normal idea of how things work will come as unexpected or surprising to you.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
あなた弟と妹がいるの？意外だね。
Oh, you have a brother and a sister. That's unexpected.
意外と体重は落ちてた。
Unexpectedly, my weight has dropped.
ゆですぎの柔らかいパスタを好んで食べるのは、カナダの意外な文化でした。
Liking soft pasta that's been cooked too long was an unexpected aspect of Canadian culture.