- To happen or take place.
"The liftoff will occur in exactly twelve seconds."
- (sciences) To be present or found.
"The chemical monofluoroacetate occurs in all parts of Dichapetalum cymosum, and is responsible for its toxic effects."
- (impersonal) To come or be presented to the mind; to suggest (itself).
- To present or offer (itself).
"I will write if the opportunity occurs."