carnival vs red letter day

carnival

noun
  • A festive occasion marked by parades and sometimes special foods and other entertainment. 

  • Any of a number of festivals held just before the beginning of Lent. 

  • A traveling amusement park, called a funfair in British English. 

red letter day

noun
  • A particularly significant day; a day of personal or sectarian celebration. 

  • A day marked in red on calendars; a church feast day. 

How often have the words carnival and red letter day occurred in a corpus of books? (source: Google Ngram Viewer )