upside vs zenith

upside

noun
  • The highest or uppermost side or portion of something. 

  • An upward tendency, especially in a financial market etc. 

  • A favourable aspect of something that also has an unfavourable aspect. 

prep
  • On the top of. 

zenith

noun
  • Highest point or state; peak. 

  • The point in the sky vertically above a given position or observer; the point in the celestial sphere opposite the nadir. 

  • The highest point in the sky reached by a celestial body. 

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