napkin vs tea napkin

napkin and tea napkin both are nouns.

Word	Noun	Adjective	Verb	Adverb
napkin	Yes	No	No	No
tea napkin	Yes	No	No	No

As nouns, tea napkin is a hyponym of napkin; that is, tea napkin is a word with a more specific, narrower meaning than napkin:

napkin: a small piece of table linen that is used to wipe the mouth and to cover the lap in order to protect clothing
tea napkin: a small napkin used when tea is served

Other hyponyms of napkin include bib, dinner napkin.

napkin (noun)	tea napkin (noun)
a small piece of table linen that is used to wipe the mouth and to cover the lap in order to protect clothing	a small napkin used when tea is served
garment consisting of a folded cloth drawn up between the legs and fastened at the waist; worn by infants to catch excrement