coincidence

Concise Oxford English Dictionary © 2008 Oxford University Press:
coincidence/kəʊˈɪnsɪdəns/

▶noun

• 1 a remarkable concurrence of events or circumstances without apparent causal connection.

• 2 correspondence in nature or in time of occurrence.

• 3 Physics the presence of ionizing particles or other objects in two or more detectors simultaneously, or of two or more signals simultaneously in a circuit.

– derivatives
coincidental adjective,
coincidentally adverb.