clear as a bell vs unclear

clear as a bell

adj
  • Totally clear; distinct and unmistakeable, as a bell's tone is clearly heard. 

unclear

verb
  • To undo the process of clearing. 

adj
  • Not easy to see or read; indecipherable or unreadable. 

  • Ambiguous; liable to more than one interpretation. 

  • Not having a clear idea; uncertain. 

  • Not clearly or explicitly defined. 

How often have the words clear as a bell and unclear occurred in a corpus of books? (source: Google Ngram Viewer )