bi•lat•eralBrE /ˌbaɪˈlætərəl/NAmE /ˌbaɪˈlætərəl/adjective 1 involving two groups of people or two countriesbilateral relations/agreements/trade/talks 2 (medical) involving both of two parts or sides of the body or brainbilateral hearing impairment bi•lat•eral•ly /BrE ˌbaɪˈlætərəli; NAmE ˌbaɪˈlætərəli/ adverb compare multilateral, trilateral, unilateral