Chance occurrence refers to something that happens unexpectedly or by luck. There are several synonyms for this word that describe similar experiences. Coincidence refers to two or more things happening at the same time that seem to be connected, but not necessarily caused by each other. Happenstance is a similar term that describes an event or situation that happens by chance, rather than by design. Serendipity is another term that refers to a happy coincidence, where a person discovers something unexpected while looking for something else. Fate, fortune, and luck are also synonyms that describe the idea of chance occurrence.