commemoration vs saint's day

commemoration

noun
  • The act of commemorating; an observance or celebration to honor the memory of some person or event. 

  • The great festival of the Oxford academic year, usually taking place on the third Wednesday after Trinity Sunday. 

  • That which serves the purpose of commemorating; a memorial. 

  • The specification of individual saints in the prayers for the dead. 

saint's day

noun
  • A day in a liturgical calendar that is observed in honour of a saint; not necessarily a holiday. 

How often have the words commemoration and saint's day occurred in a corpus of books? (source: Google Ngram Viewer )