Unilateral means "involving, affecting, obligating, or recognizing one side only" of two or more parties, persons, or nations. Bilateral applies to two sides rather than one. For example, a bilateral agreement is binding on both parties, a unilateral agreement on only one. When two nations reach a bilateral decision, responsibility for it is shared. When a country acts independently, it does so in a unilateral way.
Dictionary of problem words and expressions. Harry Shaw. 1975.