- a dimension in addition to length, width, and depth, used so as to be able to employ geometrical language in discussing phenomena that depend on four variables: Time is considered a fourth dimension for locating points in space-time.
- something beyond the kind of normal human experience that can be explained scientifically: The story deals with ESP and other excursions into the fourth dimension.
- the dimension of time, which is necessary in addition to three spatial dimensions to specify fully the position and behaviour of a point or particle
- the concept in science fiction of a dimension in addition to three spatial dimensions, used to explain supernatural phenomena, events, etc
