What does bilaterally mean?
Bilaterally is a formal adverb meaning in a manner involving two sides, whether those sides are negotiating nations, opposing parties to a dispute, or the left and right halves of the human body. Its dominant use lies in diplomacy and international relations: when countries settle matters bilaterally, they do so directly with each other rather than through a larger multilateral forum such as the United Nations. The word also has an established role in anatomy and medicine, where it indicates that a condition, symptom, or structure occurs on both sides of the body — for instance, hearing loss present bilaterally. Derived from Latin roots meaning 'two-sided', it carries a neutral, technical connotation and appears chiefly in news reporting, legal texts, and clinical documentation. It contrasts naturally with unilaterally (one side acting alone) and multilaterally (many parties acting together), making it a precise term for describing who is involved in any joint action.
In a way that involves or affects two sides; by mutual action between two parties.
"The border question was settled bilaterally through months of quiet diplomacy."
Especially common in political and legal contexts describing agreements made directly between two states or organizations.
(Anatomy/medicine) On both sides of the body.
"The swelling was observed bilaterally in the ankles during examination."
In clinical usage this term flags findings that affect both the left and right sides, often relevant to diagnosis.
Swap one prefix and the whole diplomatic world changes: 'bilaterally' means two sides talking; 'unilaterally' means going it alone — the difference between a treaty and a tantrum.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of bilaterally
Bilaterally derives from the adjective 'bilateral', formed from the Latin prefix bi- ('two') and lateralis ('of or belonging to the side'), itself from latus ('side'). The adjective entered English around the mid-nineteenth century, particularly in scientific and anatomical writing, with the adverb following shortly after. It shares this root with related terms built on latus/lateralis, including lateral, unilateral, and multilateral, all coined using the same Latinate pattern of combining prefixes with 'lateral'.
Related word forms
How bilaterally is actually used
Formal register, most common in diplomacy, law, and medicine. In medical contexts it specifically signals that a condition or finding appears on both sides of the body, which can carry diagnostic significance.
Easily confused with bilaterally
'Bilateral' is an adjective describing something with two sides (e.g. bilateral talks), while 'bilaterally' is the adverb describing how an action is done.
'Unilaterally' means acting on one side alone without agreement from others, whereas 'bilaterally' involves both parties together.