rigamajig vs whatsit

rigamajig

noun
  • A thingy; a miscellaneous or nameless object. 

whatsit

noun
  • A thing (used in a vague way to refer to something whose name one cannot recall, or that one is embarrassed to say) 

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