Things that are coincidental take place at the same time, but there isn't any connection. It's just chance — a coincidence. Sometimes things seem connected because they happen at the same time, but they really aren't: they're just coincidental.

What is a word for when something happens?

Some common synonyms of event are circumstance, episode, incident, and occurrence. While all these words mean "something that happens or takes place," event usually implies an occurrence of some importance and frequently one having antecedent cause.

What is a synonym for coincidentally?

Synonyms:random, arbitrary, spontaneous, accidental, instinctive, involuntary, unintended, impromptu, coincidental, by accident.