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

Approved by frequent travelers, this portable device will effectively set your mind at ease when attempting to enjoy a restful vacation away from potential threats and unknown cameras. — Merrell Readman, Travel + Leisure, 30 Sep. 2026

An official of Congo's ruling party UDPS, Marie-Célestin Karondwa, was attacked by unknown suspects Sunday for defending the government's measures against Ebola on a radio program and was in critical condition, according to the UDPS. — Arkansas Online, 29 Sep. 2026

Noun

Even more precise measurements of all of the major unknowns in cosmology are already underway, as the Simons Observatory – a new high precision CMB telescope – makes its first observations. — Cara Giovanetti, The Conversation, 25 Sep. 2026

There’s an aspect of insecure masculinity—also present in the Turgenev and Davis Singers—as these men find themselves in the unknowns of a national transition. — James Folta, Literary Hub, 23 Sep. 2026

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
• 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