unilateral

adjective | \ ˌyü-nə-ˈla-tə-rəl \ | uni·lat·er·al

1. : done or undertaken by one party a unilateral 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 especially because the other has already performed (as by paying an amount) an option contract is unilateral