# unknown

/ənˈnoʊn/ (US) · /ʌnnˈəʊn/ (UK)

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

## Senses

### 1. not identified

adjective · CEFR B2

not known, identified, or familiar to people.

For teachers: not known, identified, or familiar; often used postpositionally in specific phrases like 'reasons unknown'.

- The letter was sent by an unknown person with no return address.
- The painting was attributed to an unknown artist from the seventeenth century, though recent stylistic analysis suggests a student of Rembrandt.

### 2. the mysterious or unexplored

noun · CEFR B2

a place, situation, or fact that nobody knows anything about yet.

For teachers: an unexplored or unidentified place, situation, or realm of knowledge; often used with the definite article 'the'.

- Space travel is a journey into the unknown for most of us.
- The explorers faced the great unknown with a mixture of trepidation and scientific curiosity, unsure of what the deep-sea trenches might reveal.

### 3. a person without fame

noun · CEFR C1 · Formal

a person who is not famous or whose identity is not known.

For teachers: an individual who lacks fame, social standing, or a public identity.

- He was a complete unknown before he won the national talent show.
- The candidate was a political unknown until a series of viral debates propelled her to the forefront of the national conversation.

### 4. math variable

noun · CEFR B2 · Technical

a symbol, like x or y, that represents a number you need to find.

For teachers: a quantity or variable in a mathematical equation whose value is initially unspecified and must be determined.

- In the equation 2x + 5 = 11, x is the unknown.
- The physicist introduced a second unknown into the formula to account for the unexpected variance in gravitational pull during the experiment.

## Examples

- The future is a great unknown.
- Entering a new market is always a risk because of the many unknowns regarding local consumer habits.
- While the technical specifications of the project are clear, the political climate remains a significant unknown that could derail the entire timeline.

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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.