cough drop vs serum

cough drop

noun
  • A small, medicated tablet intended to be dissolved slowly in the mouth to relieve coughing symptoms temporarily. 

serum

noun
  • An intensive moisturising product to be applied after cleansing but before a general moisturiser. 

  • Blood serum from the tissues of immunized animals, containing antibodies and used to transfer immunity to another individual. 

  • A watery liquid from animal tissue, especially one that moistens the surface of serous membranes or that is exuded by such membranes when they become inflamed, such as in edema or a blister. 

  • The watery portion of certain animal fluids like blood, milk, etc; whey. 

  • The clear yellowish liquid obtained upon separating whole blood into its solid and liquid components after it has been allowed to clot. 

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