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a combining form meaning “thousand” (millipede): in the metric system, used in the names of units equal to one thousandth of the given base unit (millimeter).
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Origin of milli-

<French <Latin, combining form of mille thousand
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2022


What does milli- mean?

Milli- is a combining form used like a prefix meaning “thousand.” In names of units of measure, particularly in the metric system, milli- means “one thousandth.” It is often used in scientific and technical terms.

Milli– comes from the Latin mille, meaning “thousand.” The Greek translation of mille is chī́lioi, “a thousand,” which is the source of English terms such as kilogram and kilometer. To learn more, check out our entries for both words.

Examples of milli-

An example of a word you may have encountered that features milli– is millisecond, “one thousandth of a second.”

The milli– part of millisecond literally means “thousand.” But, because second is a unit of measure (of time), here milli– means “one thousandth.” Millimeter literally means “one thousandth of a second.”

What are some words that use the combining form milli-?

What are some other forms that milli– may be commonly confused with?

Not every word that begins with the exact letters milli-, such as milliner, is necessarily using the combining form milli– to denote “thousand.” Learn why milliner means “hat-maker” at our entry for the word.

Break it down!

The combining form pede means “having a foot.” With this in mind, what does millipede literally mean?

How to use milli- in a sentence

British Dictionary definitions for milli-


denoting 10 –3millimetre Symbol: m

Word Origin for milli-

from French, from Latin mille thousand, this meaning being maintained in words borrowed from Latin (millipede)
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Medical definitions for milli-


One thousandth (10-3):millisecond.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.

Scientific definitions for milli-


A prefix that means “one thousandth,” as in millimeter, one thousandth of a meter.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.