density

density — noun

1. a measurement that compares how many people, animals, or objects are present in

1.nounB1
Definition

a measurement that compares how many people, animals, or objects are present in an area with the physical size of that area

Example

Taipei has a much higher population density than most cities in eastern Taiwan.

population density — countable units per area

The housing density in this neighbourhood is low, with large yards between each house.

Common collocations
  • population density
  • housing density
  • traffic density
  • density of + noun
  • high/low density
  • average density
  • density map
Synonyms
  • concentration

    focuses on how much of something gathers in one spot; often used for resources or chemicals rather than populations

  • compactness

    emphasises how tightly things are packed together; less formal and rarely used for scientific measurements

Antonyms
  • sparseness

    describes an area with few people or objects spread far apart

Usage Note

Commonly combined with a noun describing what is being counted: population density, housing density, traffic density. The result is usually expressed as a number per square kilometre or per hectare.

Common Mistakes

Taiwan has a high density.' (unclear what is being counted).
Taiwan has a high population density.
specify what the density refers to.
The population density is 23 million people.' (confuses total population with density).
The population density is 650 people per square kilometre.
density is a ratio, not a total count.

2. a scientific measurement of how much mass a material contains within a fixed amo

2.nounB2
Definition

a scientific measurement of how much mass a material contains within a fixed amount of space, usually expressed as grams per cubic centimetre or kilograms per cubic metre

Example

The density of water is about one gram per cubic centimetre at room temperature.

density of [substance] + measurement value

Gold's high density means a small bar can weigh several kilograms.

Common collocations
  • high/low density
  • density of + substance
  • calculate the density
  • measure the density
  • density of water/gold/air
  • density formula
  • material density
Synonyms
  • specific gravity

    compares a material's density to the density of water; used in older textbooks and some industries

  • mass per unit volume

    the full technical phrase; more precise but rarely used outside formal definitions

Antonyms
  • buoyancy

    not a true opposite; a less dense material floats in a denser one

Usage Note

In science classes, density is calculated using the formula density = mass ÷ volume. The standard SI unit is kg/m³, but g/cm³ is also common. Never use 'density' to mean simply 'heaviness' — a small piece of lead is heavy because of its high density, not because it has a lot of material overall.

Common Mistakes

Iron is heavier than wood, so it has more density.' (vague).
Iron has a higher density than wood because its atoms are packed more closely together.
density is a ratio, not a total amount of weight.
Measure the density of the box.' (wrong — box has volume but isn't a material).
Measure the density of the metal the box is made from.
density is a property of a material, not an object.

3. how packed, thick, or closely filled something is — for instance, the thickness

3.nounB2
Definition

how packed, thick, or closely filled something is — for instance, the thickness of fog, the closeness of trees in a forest, or how many ideas fit into a short piece of writing

Example

The density of the morning fog meant the airport had to delay all flights.

density of fog — natural phenomenon

Shirin noticed the density of the bamboo forest — she could barely see the sky.

Common collocations
  • density of fog/smoke
  • density of vegetation/forest
  • density of hair/fur
  • density of information
  • density of flavour/texture
  • natural density
Synonyms
  • thickness

    more informal; commonly used for fog, soup, hair, and liquids

  • heaviness

    focuses on the feeling of weight or substance; more informal, not used for vegetation

Antonyms
  • thinness

    describes something that is not dense — thin fog, thin hair, thin forest cover

Usage Note

Unlike senses 1 and 2, this sense does not involve a precise numerical measurement. It describes a subjective impression of how densely something is packed. Distinguish from sense 1 (PEOPLE PER AREA): sense 3 can apply to fog, hair, vegetation, or writing — anything that can be described as 'dense' as a quality, not just a count per unit of area.

Common Mistakes

The density of her hair is 200 strands per square centimetre.' (treating sense 3 as a precise measurement).
Her hair has a beautiful natural density
it looks very full and thick.' — sense 3 is about the quality of denseness, not a scientific number.

Word family

  • dense
    adjectiveB1
  • densely
    adverbB1
  • denseness
    nounC1

Synonym discussion

Sense: noun/1

Density, concentration, compactness, and thickness all describe how much of something fits into a given space, but they differ in scope and precision. Density is the most formal and measurable term — it implies a ratio of units per area or volume, such as population density (650 people per km²) or housing density. Concentration suggests that items gather heavily in a particular spot, with less emphasis on precise measurement; you might talk about the concentration of skyscrapers in a city's financial district or the concentration of salt in seawater. Compactness focuses on how tightly items are packed together, often describing the feel of a layout or material rather than a countable value — for example, the compactness of an old town's street plan. Thickness is the most informal and is best for fog, hair, soup, or vegetation; it reflects a sensory impression rather than a scientific figure. For a specific measurement of people per area, use density. For a sense of clustering in one place, use concentration. For the physical tightness of packing, use compactness.

density ↗concentration ↗compactnessthickness ↗

Common collocations

Nouns

  • population density
  • housing density
  • traffic density
  • material density
  • bone density

Phrases

  • high density
  • low density
  • average density
  • relative density

Prepositions

  • density of

Etymology

LatinFrenchEnglish

Density comes from Latin 'densitas', meaning 'thickness', which was formed from 'densus' ('thick, close together'). English borrowed it through French 'densité' in the early 1600s. The scientific meaning — mass per unit volume — became standard during the 18th century as chemistry and physics developed formal measurement systems. The population and housing meanings appeared later, in the 1800s, as cities grew and urban planning emerged as a field.