piece of paper vs stamp

piece of paper and stamp both are nouns.

Word	Noun	Adjective	Verb	Adverb
piece of paper	Yes	No	No	No
stamp	Yes	No	Yes	No

As nouns, stamp is a hyponym of piece of paper; that is, stamp is a word with a more specific, narrower meaning than piece of paper:

piece of paper: paper used for writing or printing
stamp: a small piece of adhesive paper that is put on an object to show that a government tax has been paid

Other hyponyms of piece of paper include slip, slip of paper, signature, folio, leaf, tear sheet, foolscap, style sheet, worksheet, revenue stamp.

piece of paper (noun)	stamp (noun)
paper used for writing or printing	a device incised to make an impression; used to secure a closing or to authenticate documents
	a block or die used to imprint a mark or design
	machine consisting of a heavy bar that moves vertically for pounding or crushing ores
	a symbol that is the result of printing or engraving
	a small adhesive token stuck on a letter or package to indicate that postal fees have been paid
	a small piece of adhesive paper that is put on an object to show that a government tax has been paid
	a type or class
	something that can be used as an official medium of payment
	the distinctive form in which a thing is made

piece of paper (verb)	stamp (verb)
	destroy or extinguish as if by stamping with the foot
	treat or classify according to a mental stereotype
	to mark, or produce an imprint in or on something
	affix a stamp to
	raise in a relief
	crush or grind with a heavy instrument
	form or cut out with a mold, form, or die
	walk heavily
	reveal clearly as having a certain character