speech vs discussion

speech and discussion both are nouns.

Word	Noun	Adjective	Verb	Adverb
speech	Yes	No	No	No
discussion	Yes	No	No	No

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

speech (noun)	discussion (noun)
the mental faculty or power of vocal communication	an exchange of views on some topic
(language) communication by word of mouth	an extended communication (often interactive) dealing with some particular topic
the act of delivering a formal spoken communication to an audience
words making up the dialogue of a play
a lengthy rebuke
the exchange of spoken words
your characteristic style or manner of expressing yourself orally
something spoken