An event or happening; an incident. The time at which an event occurs. A significant event. A favorable or appropriate time or juncture; an opportunity. See Synonyms at opportunity. Something that brings on or precipitates an action, condition, or event, especially the immediate cause. See Synonyms at cause. Something that provides a reason or justification; a ground. A need created by a particular circumstance: "He must buy what he has little occasion for\u201d ( Laurence Sterne). A large or important social gathering. Archaic Personal requirements or necessities. To provide occasion for; cause: "The year's annual reports occasion an especially revealing glimpse of how corporations lend . . . embellishment to the stark numbers of the comptroller's office\u201d ( Mark Muro). on occasion From time to time; now and then.