Open English Wordnet
Nouns
(n)coincidence, happenstancean event that might have been arranged although it was really accidental
(n)coincidencethe quality of occupying the same position or area in space“he waited for the coincidence of the target and the cross hairs”
(n)concurrence, coincidence, conjunction, co-occurrencethe temporal property of two things happening at the same time“the interval determining the coincidence gate is adjustable”