lexis vs cognition

lexis and cognition both are nouns.

Word	Noun	Adjective	Verb	Adverb
lexis	Yes	No	No	No
cognition	Yes	No	No	No

As nouns, cognition is a hypernym of lexis; that is, cognition is a word with a broader meaning than lexis:

lexis: all of the words in a language; all word forms having meaning or grammatical function
cognition: the psychological result of perception and learning and reasoning

Other hypernyms of lexis include knowledge, noesis.

lexis (noun)	cognition (noun)
all of the words in a language; all word forms having meaning or grammatical function	the psychological result of perception and learning and reasoning