Occurrence, event, incident, episode, circumstance are comparable when they denote something that happens or takes place.
Occurrence is the general term for something which takes place.
Event is frequently regarded as arising from an antecedent state of things and is usually applied to a more or less important or noteworthy occurrence.
An incident (compare incidental under ACCIDENTAL ) is commonly an occurrence of subordinate character or secondary importance, either a mere casual happening having little relation to major events or an occurrence that merely follows because of them.
The term may, however, be used of a single event that stands out or is marked off clearly from the other events (as in a story, a play, or a history) in its nature or significance or applied to a critical event that provokes a break in diplomatic relations between countries or suggests the possibility of war.
Episode (see also DIGRESSION ) is often used in place of incident in the sense of a single or outstanding event, but the term usually carries a stronger implication of distinctiveness or apartness from the main course than does incident.
Circumstance is used as a synonym of incident only when the latter is thought of as a specific or significant detail. The word is also occasionally used as a synonym for event in its more general sense.