post box vs vessel

post box

noun
  • A box or slot into which a courier or postal worker puts letters for a recipient to collect. 

  • A box in which post can be left by a sender to be picked up by a courier or postman (postal worker). 

vessel

noun
  • A person as a container of qualities or feelings. 

  • A craft designed for transportation through air or space. 

  • Any craft designed for transportation on water, such as a ship or boat. 

  • A container of liquid or other substance, such as a glass, goblet, cup, bottle, bowl, or pitcher. 

  • A tube or canal that carries fluid in an animal or plant. 

verb
  • To put into a vessel. 

How often have the words post box and vessel occurred in a corpus of books? (source: Google Ngram Viewer )