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

Focusing diffuse sunlight onto a millimeter-scale crystal posed its own challenge. — Sanidhya Sharma, Scientific American, 6 Aug. 2026

Microplastics are defined as plastic particles that are smaller than five millimeters. — Georgina Jedikovska, Interesting Engineering, 5 Aug. 2026

The Celestron AstroMaster 130mm offered a decent 130 millimeters of aperture — more than double many cheap department store refractors. — Damian Peach, Space.com, 4 Aug. 2026

Edge tracking In the experiment with a straight corridor of vinegar about 50 millimeters wide, flowing with the wind, the flies did not do the obvious thing and march up the middle. — Jacek Krywko, ArsTechnica, 1 Aug. 2026

Word History

Etymology

French millimètre, from milli- + mètre meter

First Known Use

1797, in the meaning defined above

Rhymes for millimeter

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

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