illegitimate vs unplain

illegitimate

adj
  • Not correctly deduced. 

  • Not sanctioned by marriage. 

  • Not authorized by good usage; not genuine. 

  • Involving the fertilization of pistils by stamens not of their own length, in heterogonously dimorphic and trimorphic flowers. 

  • Not conforming to known principles, or established or accepted rules or standards. 

  • Born to unmarried parents. 

  • Not in accordance with the law. 

verb
  • To make illegitimate. 

noun
  • A person born to unmarried parents. 

unplain

adj
  • Not plain. 

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