Definition of bilateral in the Definitions.net dictionary. Meaning of bilateral. What does bilateral mean? Information and translations of bilateral in the most comprehensive dictionary definitions resource on the web. BILATERAL definition: 1. involving two groups or countries: 2. involving two groups or countries: 3. involving two…. Learn more. The meaning of BILATERAL is affecting reciprocally two nations or parties. How to use bilateral in a sentence. Did you know? BILATERAL meaning: 1. involving two groups or countries: 2. involving two groups or countries: 3. involving two…. Learn more.