ETYM Latin dimensio, from dimensus, p. p. of dimetiri to measure out; di- = dis- + metiri to measure: cf. French dimension. Related to Measure.
1. A measure of the size of something in a particular direction, esp. length or width or height.
2. One of three coordinates that determine a position in space.
In science, any directly measurable physical quantity such as mass (M), length (L), and time (T), and the derived units obtainable by multiplication or division from such quantities.
For example, acceleration (the rate of change of velocity) has dimensions (LT-2), and is expressed in such units as km s-2. A quantity that is a ratio, such as relative density or humidity, is dimensionless.
In geometry, the dimensions of a figure are the number of measures needed to specify its size. A point is considered to have zero dimension, a line to have one dimension, a plane figure to have two, and a solid body to have three.