erratic vs screw loose

erratic

noun
  • Anything that has erratic characteristics. 

  • A rock moved from one location to another, usually by a glacier. 

adj
  • Deviating from normal opinions or actions; eccentric; odd. 

  • Unsteady, random; prone to unexpected changes; not consistent. 

screw loose

noun
  • A state of insanity or eccentricity. 

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