eldest vs firstborn

eldest

noun
  • The eldest child in a family, or individual in a group. 

adj
  • (of a hand) Having higher, or superior cards. 

  • (of a player) Receiving cards from the dealer first, before any other players. 

firstborn

noun
  • The first child to be born to a parent or family. 

adj
  • Most excellent; most distinguished or exalted. 

  • Born as the first one in a family, flock or the like. 

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