International System of Units

American  

noun

1. an internationally accepted coherent system of physical units, derived from the MKSA (meter-kilogram-second-ampere) system, using the meter, kilogram, second, ampere, kelvin, mole, and candela as the basic units SI unitsSI unit respectively of the fundamental quantities of length, mass, time, electric current, temperature, amount of substance, and luminous intensity. SI

---

Etymology

Origin of International System of Units

First recorded in 1930–35; translation of the earlier French name Système Internationale d'Unités

Example Sentences

Today, atomic transitions are the foundation on which all time measurements are built: a transition in the caesium-133 atom provides a reference value that underpins the International System of Units definition of the second.

From Nature

In the case of Planck’s constant, there’s now enough confidence in its value for it to become the basis of the International System of Units definition of the kilogram that was confirmed last May.

From Nature

The customary units we use legally are defined in terms of the International System of Units units.

From Washington Post

Henceforth, all seven units in the International System of Units, otherwise known as the S.I., will no longer be defined by material objects and instead will be defined only by abstract constants of nature.

From New York Times

And the graphic below, from 2017, below puts the redefinition in context of a larger planned overhaul of the International System of Units.

From Scientific American