Learner's definition of COINCIDENCE
1 : a situation in which events happen at the same time in a way that is not planned or expected
It was mere/pure/sheer coincidence that brought them together so far from Chicago.
By coincidence, every man in the room was named Fred.
Our meeting happened by coincidence. [=by chance]
“I'm going to Boston this weekend.” “What a coincidence! I am too.”
It was no coincidence that he quit his job at the bank a day after the robbery.
a series of strange coincidences
By a fortunate/happy coincidence, we arrived at the theater at the same time.
2 [singular], formal : the occurrence of two or more things at the same time 3 [singular], formal : the state of two or more things being the same — often + of