apropos vs either

apropos

adv
  • By the way. 

  • To the purpose; appropriately. 

  • Timely; at a good time. 

prep
  • Regarding or concerning. 

adj
  • Of an appropriate or pertinent nature. 

  • by the way, incidental 

either

adv
  • As well. 

pron
  • One or the other of two people or things. 

conj
  • Introduces the first of two (or occasionally more) options or possibilities, the second (or last) of which is introduced by “or”. 

det
  • Any one (of two). 

  • Each of two; both. 

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