flipside vs polar opposite

flipside

noun
  • The reverse, in contrast to the obverse. 

  • A necessary consequence or corollary of something that acts as a negation or counterbalance; especially one seen as opposite, or as pro versus con. 

  • The B-side of a phonograph record. 

  • The occasion when we meet again (e.g. when I return from work, etc.; said on parting); later or tomorrow. 

polar opposite

noun
  • The complete opposite, opposite in every way. 

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