1879, "instrument for stamping by hand with ink, having letters or numbers cast in vulcanized rubber," from rubber (n.1) + stamp (n.). The figurative sense of "thing or institution whose power is formal but not real" is by 1901 (on the notion of rubber-stamping "approved" or some such thing on everything given to it by the real powers). The verb is by 1889; in the figurative sense by 1912. As an adjective by 1931. Related: Rubber-stamped; rubber-stamping.
updated on October 15, 2021