A system of weights and measures originating in France, the use of which is required by law in many countries, and permitted in many others, including the United States; the system is also called by its French name,
Le Système International de Unités (abbreviated
SI). The principal unit of length is the
meter (see
Meter). From this are formed the
are, the
liter, the
stere, the
gram, etc. These units, and others derived from them, are divided decimally, and larger units are formed from multiples by 10, 100, 1,000, and 10,000. The successive multiplies are designated by the prefixes,
deka- (formerly
deca-),
hecto-,
kilo-, and
myria- (seldom used); successive parts by
deci-,
centi-, and
milli-. The prefixes
mega- and
micro- are used to denote a multiple by one million, and the millionth part, respectively;
giga- and
nano- denote multiples of one billion (1,000,000,000) and one billionth, respectively. The prefix for one trillion (10
12) is
tera, and for one trillionth (10
-12) is
pico; for one quintillion (10
15)
peta, and for (10
-15) (one quintillionth)
femto; for (10
-18)
atto. See the words formed with these prefixes in the Vocabulary. For
metric tables, see
p. 1682.
Also: Le Système International de Unités See: Meter