unilateral

adjective

uni·​lat·​er·​al ˌyü-ni-ˈla-tə-rəl 

-ˈla-trəl

1

a

: done or undertaken by one person or party

a unilateral cease-fire

b

: of, relating to, or affecting one side of a subject : one-sided

c

: constituting or relating to a contract or engagement by which an express obligation to do or forbear is imposed on only one party

2

a

: having parts arranged on one side

a unilateral raceme

b

: occurring on, performed on, or affecting one side of the body or one of its parts

unilateral exophthalmos

3

: unilineal

4

: having only one side

unilaterally adverb

Did you know?

The world is a smaller place than it used to be, and we get uncomfortable when a single nation adopts a policy of unilateralism—that is, acting independently with little regard for what the rest of the world thinks. A unilateral invasion of another country, for instance, usually looks like a grab for power and resources. But occasionally the world welcomes a unilateral action, as when the U.S. announced unilateral nuclear-arms reductions in the early 1990s. Previously, such reductions had only happened as part of bilateral ("two-sided") agreements with the old Soviet Union. Multilateral agreements, on issues such as climate change, often involve most of the world's nations.

Examples of unilateral in a Sentence

Our country is prepared to take unilateral action.

Recent Examples on the Web

Latin American leaders rejected the unilateral use of military force against the South American country. —Bart Jansen, USA Today, 8 Jan. 2026

Any unilateral invasion is a pretext for any other unilateral invasion, which is why each must always be repudiated, regardless of the moral justification. —Chicago Tribune, 8 Jan. 2026

The unilateral interceptions could complicate Ukraine peace talks between the US and Russia, which is said to use a fleet of shadow tankers to circumvent Western sanctions. —J.d. Capelouto, semafor.com, 7 Jan. 2026

Whatever language is used to describe it — counter-narcotics, stabilization, transition — this was an act of war, undertaken without the constitutional mechanisms designed to restrain exactly this kind of unilateral executive action. —Jon Duffy, Mercury News, 6 Jan. 2026

Word History

First Known Use

1802, in the meaning defined at sense 1a

Rhymes for unilateral

• basolateral
• contralateral
• dorsolateral
• equilateral
• ipsilateral
• multilateral
• quadrilateral
• ventrolateral
• anterolateral
• posterolateral
• bilateral
• collateral

Kids Definition

unilateral

adjective

uni·​lat·​er·​al ˌyü-ni-ˈlat-ə-rəl 

-ˈla-trəl

: done or carried out by only one of two or more parties

unilateral disarmament

unilaterally

-ē

adverb

Medical Definition

unilateral

adjective

uni·​lat·​er·​al ˌyü-ni-ˈlat-ə-rəl, -ˈla-trəl 

: occurring on, performed on, or affecting one side of the body or one of its parts

unilateral exophthalmos

unilaterally

-ē 

adverb

Legal Definition

unilateral

adjective

uni·​lat·​er·​al ˌyü-nə-ˈla-tə-rəl 

1

: done or undertaken by one party

a unilateral mistake as to the terms

2

: of, relating to, or affecting one side of a subject

3

: containing a promise to perform made by only one party especially because the other has already performed (as by paying an amount)

an option contract is unilateral

unilaterally adverb