n.1. A measure of spatial extent, especially width, height, or length.
2. often dimensions Extent or magnitude; scope: a problem of alarming dimensions.
3. Aspect; element: "He's a good newsman, and he has that extra dimension" (William S. Paley).
4. Mathematics a. The least number of independent coordinates required to specify uniquely the points in a space.
b. The range of such a coordinate.
5. Physics A physical property, such as mass, distance, time, or a combination thereof, regarded as a fundamental measure of a physical quantity: Velocity has the dimension of distance divided by time.
6. A realm of existence, as in a work of fiction, that is physically separate from another such realm: "Although it tells a grounded, political story free from aliens and alternate dimensions, the film remains packed to the brim with iconic ... characters." (Conner Schwerdtfeger).