sleet vs watch glass

sleet

noun
  • A smooth coating of ice formed on ground or other objects by freezing rain. 

  • Precipitation in the form of a mixture of rain and snow. 

  • Part of a mortar extending from the chamber to the trunnions. 

  • Pellets of ice made of mostly frozen raindrops or refrozen melted snowflakes. 

verb
  • To be in a state in which sleet is falling. 

watch glass

noun
  • An item of glass laboratory equipment consisting of a simple, slightly concave circle of glass. It is a general utility item, used to hold small samples, to evaporate liquids, to cover a beaker, and so on. 

  • A sandglass. 

  • The glass covering of the face of a watch. 

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