›(also formalpostage stamp)a small piece of paper with a picture or pattern on it, that you stick onto a letter or package to pay for the cost of mailing it: first-class/second-class stamp
›a tool used to put a date, an address, or other mark on a document or an object, usually as proof of something: The assistant uses a stamp to sign his boss's name.
›an official mark put on something that shows a date, an address, or other information: Look for the official USDA stamp before you buy.
stamp of approval›approval from someone in a position of authority: The Board will meet Thursday to discuss the contract and is likely to give its stamp of approval Friday.The foreign-made goods still have not earned the government's stamp of approval.