adj. Of, on, relating to, involving, or affecting only one side: "a unilateral advantage in defense” ( New Republic). adj. Performed or undertaken by only one side: unilateral disarmament. adj. Obligating only one of two or more parties, nations, or persons, as a contract or an agreement.adj. Emphasizing or recognizing only one side of a subject.adj. Having only one side.adj. Tracing the lineage of one parent only: a unilateral genealogy. adj. Botany Having leaves, flowers, or other parts on one side only.