leading vs unknown

leading

noun
  • Vertical space added between lines; line spacing. 

  • An act by which one is led or guided. 

adj
  • Providing guidance or direction. 

  • Occurring in advance; preceding. 

  • Ranking first. 

unknown

noun
  • A variable (usually x, y or z) whose value is to be found. 

  • A person of no identity; a nonentity 

  • Any thing, place, or situation about which nothing is known; an unknown fact or piece of information. 

adj
  • Not known; unidentified; not well known. 

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