observance vs viewport

observance

noun
  • Observation or the act of watching. 

  • The practice of complying with a law, custom, command or rule. 

  • That which is to be observed. 

  • A rule governing a religious order, especially in the Roman Catholic church. 

  • The custom of celebrating a holiday or similar occasion. 

  • Reverence; homage. 

viewport

noun
  • A viewing window. 

  • A typically rectangular region representing the range or area currently visible (within a window, screen, etc.). 

verb
  • To clip (an image or region) so that it fits in a viewport. 

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