either vs otherwise

either

adv
  • As well. 

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. 

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

otherwise

adv
  • In all other respects. 

  • Differently, in another way. 

  • In different circumstances; or else. 

adj
  • Other than supposed; different. 

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