topic vs res judicata

topic and res judicata both are nouns.

Word	Noun	Adjective	Verb	Adverb
topic	Yes	No	No	No
res judicata	Yes	No	No	No

As nouns, res judicata is a hyponym of topic; that is, res judicata is a word with a more specific, narrower meaning than topic:

Other hyponyms of topic include area, blind spot, remit, res adjudicata.

topic (noun)	res judicata (noun)
some situation or event that is thought about	a matter already settled in court; cannot be raised again
the subject matter of a conversation or discussion