alderman vs councillor

alderman

noun
  • A member of a municipal legislative body in a city or town. 

  • A long pipe for smoking. 

  • A potbelly, paunch. 

councillor

noun
  • A member of a council. 

  • In particular, a representative elected to a local authority, such as a city council: a city councillor 

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