faucet vs petcock

faucet

noun
  • An exposed plumbing fitting; a tap or spigot; a regulator for controlling the flow of a liquid from a reservoir. 

  • One or several systems that inject currency into the game's economy, thus controlling or preventing inflation 

petcock

noun
  • A small valve, spout, or faucet operated by hand, usually used to release pressure or drain fluid. 

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