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

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

Earlier research demonstrated that microcombs could produce a single precise millimeter wave frequency.

From Science Daily ● Aug. 24, 2026

The other scientist insisted “I don’t believe a half of a millimeter really matters so much.”

From The Wall Street Journal ● Aug. 24, 2026

"The millimeter and submillimeter radio bands remain almost completely unexplored for SETI, so this is really about opening up a new area of parameter space to search."

From Science Daily ● Jul. 30, 2026

That’s the scale of an atom: one ten-millionth of a millimeter.

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

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

From Barron's ● Oct. 14, 2026

They were also able to inject different substances at separate depths, with delivery points spaced almost three millimeters apart.

From Science Daily ● Sep. 21, 2026

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

From The Wall Street Journal ● Sep. 10, 2026

“Combine 2 millimeters of rain with 35 degrees Centigrade—it’s bonkers,” O’Malley said.

From The Wall Street Journal ● Aug. 31, 2026

Right now the Appalachians are shrinking on average by 0.03 millimeters per year.

From "A Walk in the Woods" by Bill Bryson

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