ambulance vs emergency room

ambulance

noun
  • An emergency vehicle designed for transporting seriously ill or injured people to a hospital. 

  • A mobile field hospital. 

verb
  • To transport by ambulance. 

emergency room

noun
  • A department of a hospital where seriously ill or injured patients, often with life-threatening conditions that require urgent or immediate treatment, are brought in, usually by ambulance. 

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