lemma vs lexical item

lemma

noun
  • The theoretical abstract conceptual form of a word, representing a specific meaning, before the creation of a specific phonological form as the sounds of a lexeme, which may find representation in a specific written form as a dictionary or lexicographic word. 

  • The outer shell of a fruit or similar body. 

  • One of the specialized bracts around the floret in grasses. 

  • The canonical form of an inflected word; i.e., the form usually found as the headword in a dictionary, such as the nominative singular of a noun, the bare infinitive of a verb, etc. 

  • A proposition proved or accepted for immediate use in the proof of some other proposition. 

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. 

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