bilateral

adjective

bi·​lat·​er·​al (ˌ)bī-ˈla-t(ə-)rəl 

1

: affecting reciprocally two nations or parties

a bilateral treaty

a bilateral trade agreement

2

: having two sides

dealing with a bilateral problem

3

biology

a

: of, relating to, or affecting the right and left sides of the body or the right and left members of paired organs

bilateral nephrectomy

b

: having bilateral symmetry

bilateralism

(ˌ)bī-ˈla-t(ə-)rə-ˌli-zəm 

noun

bilaterally adverb

Did you know?

Since the prefix bi- means "two" in Latin, bilateral means essentially "two-sided". In the days when there were two superpowers, the U.S. and the Soviet Union regularly engaged in bilateral arms negotiations; such negotiations are much less common today. Sometimes bilateral refers to two sides of the same thing. A bilateral hip replacement, for instance, replaces both hip bones in the same operation. And bilateral symmetry (a term often used by biologists) refers to the fact that, in many organisms (such as humans), the left side is basically the mirror image of the right side.

Examples of bilateral in a Sentence

Recent Examples on the Web

This has resulted in a sustained and persistent tension in their bilateral relations since Pakistan’s independence in 1947. —Rabia Akhtar, The Conversation, 20 Mar. 2026

The lineup also includes the SXSW-premiering survival documentary The Ascent, which follows a bilateral amputee attempting to climb Mount Kilimanjaro, as well as the world premiere of The Strawberry, a drama from the Plummer Brothers starring M*A*S*H actor Mike Farrell. —Andreas Wiseman, Deadline, 19 Mar. 2026

Trump has never appreciated multilateral alliances and organizations, preferring their bilateral counterparts instead. —Naomi Lim, The Washington Examiner, 18 Mar. 2026

Trump has vacillated between indifference and contempt for the USMCA, at times threatening to pull out of the agreement altogether and work instead to negotiate two separate, bilateral deals with Mexico and Canada. —Kate Nishimura, Sourcing Journal, 18 Mar. 2026

Word History

First Known Use

1751, in the meaning defined at sense 1

Phrases Containing bilateral

• bilateral symmetry

Rhymes for bilateral

• collateral
• trilateral
• anterolateral
• posterolateral
• basolateral
• contralateral
• dorsolateral
• equilateral
• ipsilateral
• multilateral
• quadrilateral
• unilateral

Kids Definition

bilateral

adjective

bi·​lat·​er·​al (ˈ)bī-ˈlat-ə-rəl 

-ˈla-trəl

1

: having or involving two sides or parties

a bilateral treaty

2

: characterized by bilateral symmetry

bilaterally

-ē

adverb

Medical Definition

bilateral

adjective

bi·​lat·​er·​al (ˈ)bī-ˈlat-ə-rəl, -ˈla-trəl 

1

: of, relating to, or affecting the right and left sides of the body or the right and left members of paired organs

bilateral nephrectomy

bilateral tumors of the adrenal glands

2

: having bilateral symmetry

bilateralism

-ˌiz-əm 

noun

bilaterality

(ˈ)bī-ˌlat-ə-ˈral-ət-ē, -ˌla-ˈtral- 

noun

plural bilateralities

bilaterally

(ˈ)bī-ˈlat-ə-rə-lē, -ˈla-trə-lē 

adverb

Legal Definition

bilateral

adjective

bi·​lat·​er·​al ˌbī-ˈla-tə-rəl 

: affecting, obligating, or shared by both parties

bilaterally

-rə-lē

adverb