unknown

1 of 2

adjective

un·​known ˌən-ˈnōn 

1

a

: not known

It was a world and life, a way of being, utterly unknown to me.

—Avi

An unknown number of cases go unreported.

For some unknown reason, the computer crashed.

b

: not well-known

an unknown writer/artist

When he left, he had been unknown. Now he was famous.

—E. B. White

2

: having an unknown value

an unknown quantity

unknown

2 of 2

noun

1

a

: one that is not known or not well-known

especially : a person who is little known (as to the public)

The director cast an unknown in the lead role.

b

the unknown : a place, situation, or thing that is not known or understood

explorers venturing into the unknown

c

: something that is not known or not yet discovered

There are too many unknowns to go forward with the project.

2

a

: a symbol (such as x, y, or z) in a mathematical equation representing an unknown quantity

b

: a specimen (as of bacteria or mixed chemicals) required to be identified as an exercise in appropriate laboratory techniques

Synonyms of unknown

Adjective

• unfamiliar
• unbeknownst

Examples of unknown in a Sentence

Adjective

a disease of unknown cause

Much remains unknown about his early life.

Her music was previously unknown outside of Asia.

An unknown number of cases go unreported.

The victim's attacker was unknown to her.

For some unknown reason, my computer crashed.

a book of unknown poems

Noun

explorers venturing off into the unknown

A fear of the unknown kept her from changing jobs.

The director cast an unknown in the lead role.

We're facing too many unknowns.

Recent Examples on the Web

Adjective

In the latest twist in human evolution, scientists have discovered that a mysterious foot found in Ethiopia belonged to a previously unknown ancient relative. —Elmira Aliieva, NBC news, 27 Nov. 2025

The cause of the fire remains unknown. —Sujita Sinha, Interesting Engineering, 27 Nov. 2025

Noun

To resolve those unknowns, the team’s next step is to pinpoint how the worm’s sulfide armor forms at the molecular level. —New Atlas, 16 Nov. 2025

On one wall was an oil painting of a ship, artist unknown. —Alice Gregory, New Yorker, 16 Nov. 2025

Word History

First Known Use

Adjective

before the 12th century, in the meaning defined at sense 1a

Noun

14th century, in the meaning defined at sense 1a

Phrases Containing unknown

• big unknown
• fear of the unknown
• For some unknown reason
• of unknown origin
• the unknown
• unknown quantity
• unknown to

Rhymes for unknown

• alone
• atone
• backbone
• bemoan
• bluestone
• breastbone
• brownstone
• capstone
• cheekbone
• condone
• curbstone
• cyclone

Kids Definition

unknown

1 of 2 adjective

un·​known ˌən-ˈnōn 

: not known

also : having an unknown value

an unknown quantity

unknown

2 of 2 noun

1

: something that is unknown

2

: a symbol (as x, y, or z) representing a quantity whose value is unknown

an equation with two unknowns