unilateral

adjective

uni·​lat·​er·​al ˌyü-ni-ˈla-tə-rəl 

-ˈla-trəl

1

a

: done or undertaken by one person or party

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

The Senate's decision marks a clear victory for the White House and shows how much latitude both Republicans and some Democrats are willing to give Trump to take unilateral military action against Iran. —Martha McHardy, MSNBC Newsweek, 28 June 2025

This matrix of deterrents – nuclear capability, US regional alliances, and Russian backing – likely insulates Pyongyang from the kind of unilateral military action Washington exercised in Iran. —Brad Lendon, CNN Money, 25 June 2025

Trump and his advisers seem to believe that, despite the country’s allegedly parlous condition, unilateral action on Washington’s part can still force others to capitulate and submit to American terms. —Kori Schake, Foreign Affairs, 24 June 2025

President Donald Trump’s decision to bomb Iran has reignited a decades-long debate over the legality of unilateral military action. —Brendan Rascius, Miami Herald, 24 June 2025

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