millième

Millième is the French term for the unit fraction one thousandth (1/1000). It also functions as an ordinal form indicating the thousandth item in a sequence, for example le millième élément. In mathematics and measurement contexts, a quantity expressed as a millième represents 0,001 of a given unit, such as un millième de mètre equals 0,001 m.

Etymology: The word derives from mille, thousand, with the suffix -ème used to form ordinal numerals in French. The form has been in use in mathematical and scientific vocabulary since medieval times.

Usage: In spoken French, very small fractions are usually expressed using decimal fractions or dedicated unit names (millimètre, milligramme, milliseconde). The phrase un millième de X is correct and unambiguous, but in technical writing it is common to prefer the precise unit name (for example, millimètre instead of millième de mètre). When referring to time, 0,001 s is often called a milliseconde rather than a millième de seconde, though the latter is understandable.

Relation to prefixes: The term millième is related to the metric prefix milli-, which designates a factor of 10^-3. The prefix is widely used to name subunits (millimètre, milligramme, millisecond), while millième refers specifically to the one-thousandth fraction or ordinal position rather than the prefix itself.

See also: milli- prefix, millimeter, millisecond, millilitre.