co-wife vs helpmate

co-wife

noun
  • In a polygamous marriage, another wife of a woman’s husband. 

helpmate

noun
  • A wife or spouse. 

  • A person who supplies help or companionship. 

  • A recreational problem in chess in which both sides cooperate to achieve a specific goal. 

How often have the words co-wife and helpmate occurred in a corpus of books? (source: Google Ngram Viewer )