lemma vs rationale

lemma

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

  • 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. 

  • 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. 

rationale

noun
  • A justification or rationalization for something. 

  • An explanation of the basis or fundamental reasons for something. 

  • A liturgical vestment worn by some Christian bishops of various denominations. 

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