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The prefix milli-, likewise, may be added to metre to indicate division by one thousand; one millimetre is equal to one thousandth of a metre. Decimal multiplicative prefixes have been a feature of all forms of the metric system , with six of these dating back to the system's introduction in the 1790s.
Milli (symbol m) is a unit prefix in the metric system denoting a factor of one thousandth (10 −3). [1] Proposed in 1793, [2] and adopted in 1795, the prefix comes from the Latin mille, meaning one thousand (the Latin plural is milia). Since 1960, the prefix is part of the International System of Units (SI).
The prefixes are never combined, so for example a millionth of a metre is a micrometre, not a millimillimetre. Multiples of the kilogram are named as if the gram were the base unit, so a millionth of a kilogram is a milligram, not a microkilogram. [5]: 122 [11]: 14 The BIPM specifies 24 prefixes for the International System of Units (SI):
A unit prefix is a specifier or mnemonic that is added to the beginning of a unit of measurement to indicate multiples or fractions of the units. Units of various sizes are commonly formed by the use of such prefixes. The prefixes of the metric system, such as kilo and milli, represent multiplication by positive or negative powers of ten.
Meaning: a prefix used to make words with a sense opposite to that of the root word; in this case, meaning "without" or "-less". This is usually used to describe organisms without a certain characteristic, as well as organisms in which that characteristic may not be immediately obvious.
The root language of a numerical prefix need not be related to the root language of the word that it prefixes. Some words comprising numerical prefixes are hybrid words. In certain classes of systematic names, there are a few other exceptions to the rule of using Greek-derived numerical prefixes.
Prefix name N/A deca hecto kilo mega giga tera peta exa zetta yotta ronna quetta; Prefix symbol da h k M G T P E Z Y R Q Factor 10 0: 10 1: 10 2: 10 3: 10 6: 10 9: 10 12: 10 15: 10 18: 10 21: 10 24: 10 27: 10 30
The United States–based Institute for Safe Medication Practices (ISMP) and the U.S. Food and Drug Administration (FDA) recommend that the symbol μg should not be used when communicating medical information due to the risk that the prefix μ (micro-) might be misread as the prefix m (milli-), resulting in a thousandfold overdose.