keynote vs topic

keynote and topic both are nouns.

Word	Noun	Adjective	Verb	Adverb
keynote	Yes	No	Yes	No
topic	Yes	No	No	No

As nouns, topic is a hypernym of keynote; that is, topic is a word with a broader meaning than keynote:

Other hypernyms of keynote include subject, theme.

keynote (noun)	topic (noun)
a fundamental or central idea	some situation or event that is thought about
(music) the first note of a diatonic scale	the subject matter of a conversation or discussion
the principal theme in a speech or literary work

keynote (verb)	topic (verb)
set the keynote of
give the keynote address to (an audience)