stamp has 17 distinct synonyms spread across 10 of its 18 senses. Each sense below keeps its own list, because a synonym belongs to a meaning and not to a word: swapping one sense's substitute into another sense's sentence is how a thesaurus makes writing worse. WordNet records no antonym for it — antonymy is a relation between word forms rather than concepts, so it is deliberately sparse.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
a type or class
“more men of his stamp are needed”
a symbol that is the result of printing or engraving
“he put his stamp on the envelope”
a small adhesive token stuck on a letter or package to indicate that that postal fees have been paid
something that can be used as an official medium of payment
a small piece of adhesive paper that is put on an object to show that a government tax has been paid
a block or die used to imprint a mark or design
to mark, or produce an imprint in or on something
“a man whose name is permanently stamped on our maps”
reveal clearly as having a certain character
“His playing stamps him as a Romantic”
treat or classify according to a mental stereotype
“I was stereotyped as a lazy Southern European”
destroy or extinguish as if by stamping with the foot
“Stamp fascism into submission”
form or cut out with a mold, form, or die
“stamp needles”
crush or grind with a heavy instrument
“stamp fruit extract the juice”
Synonyms, antonyms and the broader and narrower relations for stamp come from Princeton University’s WordNet. Full sources and licences.