so-and-so vs thingum

so-and-so

noun
  • Used in place of epithets such as SOB, bastard, etc.. 

  • Some thing or things. 

  • A placeholder name for a person or thing, used when a name is not known; a generic name. 

thingum

noun
  • Synonym of thingummy 

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