roe vs caviar

roe and caviar both are nouns.

Word	Noun	Adjective	Verb	Adverb
roe	Yes	No	No	No
caviar	Yes	No	No	No

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

roe: fish eggs or egg-filled ovary; having a grainy texture
caviar: salted roe of sturgeon or other large fish; usually served as an hors d'oeuvre

Other hyponyms of roe include coral, caviare, shad roe.

roe (noun)	caviar (noun)
eggs of female fish	salted roe of sturgeon or other large fish; usually served as an hors d'oeuvre
the eggs or egg-laden ovary of a fish
the egg mass or spawn of certain crustaceans such as the lobster
fish eggs or egg-filled ovary; having a grainy texture