labyrinth vs tough proposition

labyrinth

noun
  • Any of various satyrine butterflies of the genus Neope. 

  • A complicated irregular network of passages or paths, especially underground or covered, in which it is difficult to find one's way. 

  • An accessory respiratory organ of certain fish. 

  • A maze formed by paths separated by high hedges. 

  • Anything complicated and confusing in structure, arrangement, or character. 

  • A complex structure in the inner ear which contains the organs of hearing and balance. It consists of bony cavities (the bony labyrinth) filled with fluid and lined with sensitive membranes (the membranous labyrinth). 

verb
  • to twist and wind, following a labyrinthine path 

  • to enclose in a labyrinth, or as though in a labyrinth 

  • to render lost and confused, as if in a labyrinth 

  • to arrange in the form of a labyrinth 

tough proposition

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