process server vs warrant officer

process server

noun
  • A deliverer of processes or summonses, the formal announcements of the beginning of a legal action; a huissier de justice or other equivalent position in other legal systems. 

warrant officer

noun
  • An officer assigned to execute warrants and other writs. 

  • An officer holding rank by virtue of a warrant rather than a commission. 

How often have the words process server and warrant officer occurred in a corpus of books? (source: Google Ngram Viewer )