means A particular time or event, often one notable enough to mark or dress up for, or the reason something happens.

from From Latin 'occasio,' meaning an opportunity or chance, built on 'occidere'—'to fall down, to befall'—from 'ob-' (toward, against) plus 'cadere' (to fall), the same root that gives us 'cadence' and 'accident.' An occasion, then, was originally a thing that simply fell your way: a moment that happened to land. It reached English through Old French 'occasion,' carrying that sense of a falling-together of circumstance—a chance that arrives whether or not you sent an invitation.