once vs whilom

once

adv
  • Formerly; during some period in the past. 

  • Multiplied by one: indicating that a number is multiplied by one. 

  • One and only one time. 

conj
  • As soon as; when; after. 

whilom

adv
  • At some time in the past; formerly, once upon a time. 

conj
  • During the same time that; while. 

  • Up to the time that; till, until. 

adj
  • At some time in the past; former, sometime. 

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