1
general::
A person or organization that automatically approves or endorses a policy without assessing its merit; also, such an approval or endorsement. For example, The nominating committee is merely a rubber stamp; they approve anyone the chairman names, or The dean gave his rubber stamp to the recommendations of the tenure committee. This metaphoric term alludes to the rubber printing device used to imprint the same words over and over. [Early 1900s]
American Heritage Idioms