lexical item vs lexical unit

lexical item

noun
  • A term—word or a sequence of words—that acts as a unit of meaning, including words, phrases, phrasal verbs and proverbs, exemplified by cat, traffic light, take care of, by-the-way, and don't count your chickens before they hatch. 

lexical unit

noun
  • A pairing of a word or phrase with one of its meanings. 

How often have the words lexical item and lexical unit occurred in a corpus of books? (source: Google Ngram Viewer )