millimeter

noun

mil·​li·​me·​ter ˈmi-lə-ˌmē-tər 

variants US millimeter or British millimetre

: a unit of length equal to 1/1000 meter see Metric System Table

Examples of millimeter in a Sentence

Recent Examples on the Web

Microplastics, which are less than 5 millimeters in size, come from larger plastic pieces that degrade in the environment. —Erika Edwards, NBC news, 2 Apr. 2026

The particles, which are less than five millimeters in size, cannot be fully removed by traditional water filtration methods, according to the World Health Organization. —Kerry Breen, CBS News, 2 Apr. 2026

Even the smallest components are painted or treated to ensure maximum longevity, while final assembly (carried out after at least one dry run) aims for millimeter-perfect panel gaps, impeccable door closure, and a rattle-free ride. —Simon De Burton, Robb Report, 1 Apr. 2026

In some years, the tree grows only a few millimeters. —Big Think, 31 Mar. 2026

Word History

Etymology

French millimètre, from milli- + mètre meter

First Known Use

1797, in the meaning defined above

Rhymes for millimeter

• amphitheater
• centimeter
• centimetre
• decimeter
• ergometer
• expositor
• gasometer
• gravimeter
• hexameter
• manometer
• milliliter
• millimetre

Kids Definition

millimeter

noun

mil·​li·​me·​ter ˈmil-ə-ˌmēt-ər 

: a measure of length equal to ¹⁄₁₀₀₀ meter see metric system table

Medical Definition

millimeter

noun

mil·​li·​me·​ter

variants or chiefly British millimetre

ˈmil-ə-ˌmēt-ər 

: one thousandth of a meter

—abbreviation mm