black tar vs opiate

black tar

noun
  • An illicit drug formed from the incomplete acetylation of morphine, containing a variable percentage of heroin. 

opiate

noun
  • A drug, hormone or other substance derived from or related to opium. 

  • Something that dulls the senses and induces a false and unrealistic sense of contentment. 

adj
  • Soporific; inducing sleep or sedation. 

  • Relating to, resembling, or containing opium. 

  • Deadening; causing apathy or dullness. 

verb
  • To treat with an opiate drug. 

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