lexeme vs linguistic unit

lexeme and linguistic unit both are nouns.

Word	Noun	Adjective	Verb	Adverb
lexeme	Yes	No	No	No
linguistic unit	Yes	No	No	No

As nouns, linguistic unit is a hypernym of lexeme; that is, linguistic unit is a word with a broader meaning than lexeme:

lexeme: a minimal unit (as a word or stem) in the lexicon of a language; `go' and `went' and `gone' and `going' are all members of the English lexeme `go'
linguistic unit: one of the natural units into which linguistic messages can be analyzed

Other hypernyms of lexeme include language unit.

lexeme (noun)	linguistic unit (noun)
a minimal unit (as a word or stem) in the lexicon of a language; `go' and `went' and `gone' and `going' are all members of the English lexeme `go'	one of the natural units into which linguistic messages can be analyzed