since vs thenceforth

since

adv

  • From a specified time in the past. 

conj

  • Because. 

  • From the time that. 

prep

  • At certain points during that period of time. 

  • Continuously during that period of time. 

thenceforth

adv

  • From that time on. 

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