coincide

Coincide is a verb with several related senses. It most commonly means to occur at the same time or in the same place, or to correspond or agree in some essential respect. The term can also be used in mathematics and geometry to describe objects that share exactly the same set of points.

Etymology and forms: Coincide comes from Latin coincidere, from com- “together” and cadere “to fall.” The related forms include coincident (adjective or noun in some uses) and coinciding (present participle). The noun form coincidence refers to a remarkable or chance occurrence, not the act of overlapping itself.

Usage: Time. A meeting and a deadline can coincide, or a holiday may coincide with a weekday. Place. Two roads may coincide along a stretch, meaning they lie on the same path. Agreement. A theory may coincide with observed data, indicating correspondence between prediction and evidence. Mathematics and geometry. Two geometric objects coincide if they are identical in all points; in coordinate terms, their representations overlap exactly. In statistics, different measurements may coincide within experimental error.

Prepositions and phrases: Coincide with is the most common construction (The dates coincide with the conference). Coincide in is used when referring to agreement in a particular respect or characteristic. Coincidence is the noun form used to denote a chance alignment or a surprising similarity, not the act of overlapping.

Related terms include coincident, coincidental, and coincidence. These differ in meaning and usage, notably between overlap, agreement, and chance correlation.