SI unit

noun

See under International System of Units.

British Dictionary definitions for si unit

SI unit

noun

any of the units adopted for international use under the Système International d'Unités, now employed for all scientific and most technical purposes. There are seven fundamental units: the metre, kilogram, second, ampere, kelvin, candela, and mole; and two supplementary units: the radian and the steradian. All other units are derived by multiplication or division of these units without the use of numerical factors

Scientific definitions for si unit

SI unit

Any of the units of measure in the International System. See more at International System.