decider vs semifinal

decider

noun
  • An event or action which decides the outcome of a contested matter. 

  • A person, divinity, or authoritative text which decides. 

  • A Turing machine that halts regardless of its input. 

semifinal

noun
  • A competition that narrows a field of contestants (semifinalists) to a set of finalists, for a subsequent final. 

  • A playoff in the round with only four players or teams left, the stage before the final. 

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