unexpected, chance, coincidence

偶然(ぐうぜん)	:coincidence. This is what you say when you run into an old acquaintance on the street.

意外(いがい)	Unexpected. “Her death was quite unexpected.” Also means, “contrary to expectations.”

案外(あんがい)	More than one expected. “I think you’ll find becoming a police detective is going to be harder than you expected.”