onethousandth

Onethousandth is not a standard single-word form in English. The conventional spellings are one thousandth or one-thousandth. The term can refer to either a fraction, 1/1000, or the ordinal position in a sequence at number 1000.

In mathematics, one thousandth equals 0.001 in decimal form and is the reciprocal of 1000. As a fraction, it is a unit fraction: 1/1000. It is used to express very small parts of a whole, such as dividing a whole into a thousand equal parts.

In the metric system, the prefix milli- denotes 10^-3, so a millimeter is one thousandth of a meter, and a milliliter is one thousandth of a liter. Percentages can also describe thousandths; 0.1% equals 0.001, i.e., one thousandth.

As an ordinal, the thousandth (the 1000th) refers to the position numbered 1000 in a sequence. The term is commonly used in mathematics, science, and measurements, and is contrasted with the decimal places referred to as tenths, hundredths, and thousandths.