mail boat vs packet boat

mail boat

packet boat

noun
  • A boat specifically designed to provide transportation to passengers on a regular schedule up and down a river or canal. 

  • A boat that carried mail, cargo, and, in later years, some passengers along a regularly scheduled route up and down a river or canal. 

  • An ocean-going ship chartered by the government to carry the mail and official communications. 

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