figment of one's imagination vs imaginary

figment of one's imagination

noun
  • A product of the imagination. 

imaginary

noun
  • Imagination; fancy. 

  • The set of values, institutions, laws, and symbols common to a particular social group and the corresponding society through which people imagine their social whole. 

  • An imaginary quantity. 

adj
  • Existing only in the imagination. 

  • Having no real part; that part of a complex number which is a multiple of √ (called imaginary unit). 

How often have the words figment of one's imagination and imaginary occurred in a corpus of books? (source: Google Ngram Viewer )