millimeter

American  

[mil-uh-mee-ter] / ˈmɪl əˌmi tər /

especially British, millimetre

noun

• millimeters
  plural

1. a unit of length equal to one thousandth of a meter and equivalent to 0.03937 inch. mm

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millimeter Scientific  

/ mĭl′ə-mē′tər /

1. A unit of length in the metric system equal to 0.001 meter.

2. See Table at measurement

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Other Word Forms

Derived Forms

• millimetric
  adjective

Inflected Forms

Nouns

• millimeters
  plural

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Etymology

Origin of millimeter

First recorded in 1800–10; from French millimètre; see milli-, meter ¹

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Explanation

A millimeter is a tiny unit of measurement. The thickness of a dime is a little more than a millimeter, and there are a thousand millimeters in a meter. If you're using metric units to measure the length of something, you'll be dealing in meters and variations on meters, including millimeters. Look at a ruler that includes centimeters, the units of metric measurement that are closest in length to inches. The smallest units marked on the ruler are millimeters — there are ten of them in each centimeter. Although the word millimeter sounds like "million," it actually means "thousandth of a meter."

Example Sentences

See Examples For:

millimeter millimeters

The finished fiber measures less than half a millimeter across.

From Science Daily ● Sep. 21, 2026

The researchers eventually made progress using electron cryotomography, a high-resolution 3D imaging method capable of revealing structures at the scale of a millionth of a millimeter.

From Science Daily ● Sep. 3, 2026

They grow about a centimeter or two a year and by sampling cores at the millimeter scale, the team was able to develop windows of monthly temperature records scattered across the past millennium.

From Barron's ● Aug. 27, 2026

"That has paid off really well for us because there are a lot of people out there that are seeking that 70 millimeter presentation."

From Barron's ● Jul. 26, 2026

For a terrible moment, Woolf clung to Seabiscuit’s neck, a millimeter from falling off, then regained his balance.

From "Seabiscuit: An American Legend" by Laura Hillenbrand

They also had to be in direct contact -- a few millimeters apart, and nothing significant happened.

From Barron's ● Oct. 14, 2026

A reading of 120 over 80, measured in millimeters of mercury, could indicate prehypertension.

From The Wall Street Journal ● Oct. 11, 2026

As those materials move, Earth's center of mass circles around its geometric center by as much as several millimeters.

From Science Daily ● Oct. 7, 2026

Google’s Pixel 11 Pro Fold is 239 grams and 10.1 millimeters.

From The Wall Street Journal ● Sep. 10, 2026

A typical paramecium, for instance, is about two microns wide, 0.002 millimeters, which is really very small.

From "A Short History of Nearly Everything" by Bill Bryson

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