fading vs perpetual

fading

noun
  • The process by which something fades; gradual diminishment. 

perpetual

adj
  • Set up to be in effect or have tenure for an unlimited duration. 

  • Continuing; uninterrupted. 

  • Lasting forever, or for an indefinitely long time. 

  • Flowering throughout the growing season. 

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