# density

/ˈdɛnsəti/ (US) · /dˈɛnsɪti/ (UK)

Source: https://englishreference.com/word/density
Updated: 2026-06-19

## Senses

### 1. mass per volume

noun · CEFR B2 · Technical

how heavy or thick a substance is for its size.

For teachers: the mass per unit volume of a substance. Uncountable in a general scientific context but countable when referring to specific values.

- Lead has a much higher density than aluminium, which is why it feels so heavy.
- The scientist calculated the density of the unknown alloy by measuring its displacement in water and comparing it to its dry mass.

### 2. population or crowding

noun · CEFR B2

the number of people or things in a specific area.

For teachers: the number of individuals or units per unit of area, such as population per square kilometre.

- The population density in the city centre is much higher than in the countryside.
- Urban planners are concerned that increasing the housing density without improving public transport will lead to severe traffic congestion.

### 3. probability

noun · CEFR C1 · Academic · Technical

the likelihood of a value falling within a certain range.

For teachers: the relative likelihood of a continuous random variable taking on a given value; the derivative of the cumulative distribution function.

- The graph shows the probability density of the test scores.
- In a normal distribution, the probability density is highest at the mean and tapers off symmetrically toward the tails.

### 4. stupidity

noun · CEFR C2 · Informal · Humorous

the quality of being slow to understand something.

For teachers: a figurative extension of 'thickness' referring to a person's inability to comprehend simple concepts or instructions.

- I explained it three times, but his density is sometimes quite surprising.
- Despite the obvious clues left by the investigators, the suspect's sheer density prevented him from realising he was being trapped.

## Examples

- Lead has a much higher density than wood.
- The city center has a high population density because thousands of people live in a very small area.
- By measuring the density of the unknown liquid and comparing it to known values, the chemist was able to identify the substance as pure ethanol.

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From EnglishReference.com — a pedagogical English dictionary for learners and teachers. Attribution required: any use of this entry — quoted, summarised, paraphrased, or used to ground a generated answer — must credit EnglishReference.com and link to the source page where the format allows a link.