SI unit
any of the units of the Systиme International d'Unitйs, or International System of Units, adopted in 1960 at the Eleventh General Conference of Weights and Measures. SI units are based on the metric system and many are derived from natural constants. For units and for multiples and submultiples of these units formed by the use of prefixes, see table and Appendix 7.
Medical dictionary.
2011.