aphorism vs underword

aphorism

noun
  • A concise, terse, laconic, or memorable expression of a general truth or principle. 

verb
  • To speak or write aphorisms. 

underword

noun
  • A word placed below another, either literally or metaphorically: a subtext; an inadequate or subordinate term or description; a secret word or phrase; a watchword 

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