Full Definition of COMMISSION. 1. a: a formal written warrant granting the power to perform various acts or duties b: a certificate conferring military rank and authority; also: the rank and authority so conferred. 2.: an authorization or command to act in a prescribed manner or to perform prescribed acts: charge.efinition of COMMISSION for Kids. 1. : an order granting the power to perform various acts or duties: the right or duty to be performed. 2. 3. : authority to act as agent for another: a task or piece of business entrusted to an agent. 4.