Real Dictionary

rubber stamp
countable noun: A rubber stamp is a small device with a name, date, or symbol on it. You press it on to an ink pad and then on to a document in order to show that the document has been officially dealt with.

rubber stamp in British English
a stamp (sense 12) stamp (sense 12a) made of rubber, pressed on an inking pad and used for printing signatures, dates, emblems, etc.
routinely approved or approving
to imprint (forms, invoices, etc) with a rubber stamp
to put the impression of a rubber stamp on
noun: a device used for imprinting dates or commonly used phrases on forms, invoices, etc
noun: a device with a rubber printing surface that becomes coated with ink by being pressed on an ink-saturated pad, used for imprinting dates, addresses, standard designations or notices, etc., by hand

rubber-stamp in American English
adjective: tending to give approval automatically or without due consideration
transitive verb: to imprint with a rubber stamp