7th vs seventh

7th

seventh

noun
  • A tone of the seventh degree from a given tone, the interval between two such tones, or the two tones sounding in unison. 

  • The person or thing in the seventh position. 

  • One of seven equal parts of a whole. 

adj
  • The ordinal form of the number seven. 

How often have the words 7th and seventh occurred in a corpus of books? (source: Google Ngram Viewer )