broadly, having or involving only one side, especially describing a decision that affects only one person, group, or entity in a situation or an action that is only done by one person/group/entity;
e.g. They made the unilateral decision to go ahead with their plan without consulting the other members of their group.
(adjective)
affecting, occurring on, or relating to only one side of the body or a body part;
e.g. She suffered from unilateral injuries because the impact occurred mainly on her right side.