piety vs religion

piety

noun
  • A devout act or thought. 

  • Reverence and devotion to God. 

  • A belief that is accepted unthinkingly and with undue reverence. 

  • Similar reverence to one's parents and family or to one's country. 

religion

noun
  • A particular system of such belief, and the rituals and practices proper to it. 

  • Rituals and actions associated with religious beliefs, but considered apart from them. 

  • Any practice to which someone or some group is seriously devoted. 

  • Belief in a spiritual or metaphysical reality (often including at least one deity), accompanied by practices or rituals pertaining to the belief. 

  • The way of life committed to by monks and nuns. 

verb
  • Engage in religious practice. 

  • To make sacred or symbolic; sanctify. 

  • Indoctrinate into a specific religion. 

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