coincident

Coincident is an adjective that describes things that occur at the same time or in the same place, or that are in some sense identical or corresponding. The word derives from Latin coincidence, formed by co- meaning together and idem meaning the same. In everyday usage, it often refers to events seeming to occur simultaneously, though not necessarily by causal connection.

In mathematics and geometry, coincident describes objects that share the same position or overlap completely. Two points are coincident if they have identical coordinates. Two or more lines, curves, or shapes are coincident if they lie on top of each other. The term also appears in descriptions of objects that occupy the same location in space, such as coincident sensors or coincident points on a graph.

In other disciplines, coincident can denote simultaneous occurrence or alignment of unrelated events, such as coincident astronomical events or coincident observations in an experiment. It emphasizes temporal or spatial overlap rather than a causal relationship.

Distinctions from related forms are important: coincidental refers to happening by chance and is often used to describe events that appear related but are not caused by each other, whereas coincident focuses on the fact of overlap or agreement. The noun form is coincidence, and the related adjective is coincidental.