unilateral adj1 : done or undertaken by one party [a mistake as to the terms]
2 : of, relating to, or affecting one side of a subject
3 : containing a promise to perform made by only one party esp. because the other has already performed (as by paying an amount) [an option contract is ]
Source: Merriam-Webster's Dictionary of Law ©1996. Merriam-Webster, Incorporated. Published under license with Merriam-Webster, Incorporated.