p.m. vs post meridiem

p.m.

adv
  • after noon (used after a time to indicate it is between noon and midnight, i.e., in the afternoon, evening or night as opposed to the morning) 

  • after death 

post meridiem

adv
  • After noon, in the afternoon. 

How often have the words p.m. and post meridiem occurred in a corpus of books? (source: Google Ngram Viewer )