millimeter

millimeter — noun

1. a metric unit for measuring very short lengths or small distances. One millimete

1.nounA2
Definition

a metric unit for measuring very short lengths or small distances. One millimeter equals exactly 1/1000 of a meter — it is about as thick as a coin or a fingernail.

Example

A two-millimeter crack in the glass did not stop us from using the cup.

hyphenated compound: numeral + millimeter + noun (crack)

Charlotte measured the wooden plank carefully, cutting each end to exactly five millimeters thick.

Common collocations
  • a few millimeters
  • several millimeters
  • millimeters wide / thick / long / deep
  • millimeters in diameter
  • fractions of a millimeter
  • within a millimeter
  • accurate to the millimeter
Synonyms
  • mm

    standard written symbol; used on rulers, maps, and in technical writing instead of the full word

Grammar Patterns

number + millimeter(s) + dimension adjective (wide, thick, long, deep)

number + millimeter(s) + in + dimension noun (length, width, thickness)

Usage Note

Frequently placed after a number and before an adjective of dimension (wide, thick, long, deep, high). The plural form millimeters is used with numbers greater than one: 1 millimeter but 3 millimeters.

Common Mistakes

My pencil is 15 millimeters long.
My pencil is 15 centimeters long (150 millimeters).
A pencil is about 15 cm; mm is for tiny measurements like the pencil's diameter.
The metal is 2 millimeter thick.
The metal is 2 millimeters thick.
After any number greater than one, the unit must be plural.

Word family

Synonym discussion

Sense: noun/1

These three metric units all measure length, but each is suited to a different scale. A millimeter (mm) is tiny — about the thickness of a fingernail — and is used for small objects or precise measurements (a screw's diameter, the depth of a cut). A centimeter (cm) is ten times larger, roughly the width of a fingertip, and works well for everyday objects like a pen or a book's width. A meter (m) is one hundred centimeters and fits human-scale measurements — a door's height, a room's length, a person's height. Learners often confuse millimeter and centimeter when describing ordinary objects: a pencil is about 15 cm, not 15 mm. When in doubt, picture your hand — fingernail = mm, fingertip = cm, arm span ≈ 1 m.

millimeter ↗centimeter ↗meter ↗

Common collocations

Nouns

Phrases

  • within a few millimeters
  • accurate to the millimeter
  • fractions of a millimeter

Prepositions

Etymology

LatinGreekFrenchEnglish

The word millimeter comes from joining French milli- (meaning 'thousand', from Latin mille) with mètre (from Greek métron, meaning 'measure'). It first appeared in English in the early 1800s as the metric system spread across Europe.