One-sided; ex parte; having relation to only one of two or more persons or things. Unilateral contract. See CONTRACT. Unilateral mistake. A mistake or misun-derstanding as to the terms or effect of a contract, made or entertained by one of the parties to it but not by the other. Unilateral record. Records are unilateral when offered to show a particular fact, as a prima jade case, either for or against a stranger.