mental lexicon vs speech

mental lexicon and speech both are nouns.

Word	Noun	Adjective	Verb	Adverb
mental lexicon	Yes	No	No	No
speech	Yes	No	No	No

mental lexicon (noun)	speech (noun)
a language user's knowledge of words	the mental faculty or power of vocal communication
	(language) communication by word of mouth
	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