Meaning of “coincidence” - Learner’s Dictionary

coincidence

noun [ C, U ] us uk /kəʊˈɪnsɪdəns/

B2 a situation in which two very similar things happen at the same time but there is no reason for it:

an amazing/strange coincidence
It was pure coincidence that we both married dentists.
coincidental adjective us uk /kəʊˌɪnsɪˈdentəl/

happening by coincidence:

The similarities are coincidental.
coincidentally adverb us uk /kəʊˌɪnsɪˈdentəli/

(Definition of “coincidence” from the Cambridge Learner’s Dictionary © Cambridge University Press)