errorous vs improper

errorous

adj
  • Synonym of erroneous 

improper

adj
  • Not according to facts; inaccurate or erroneous 

  • unsuitable to needs or circumstances; inappropriate; inapt 

  • Not properly named; See, for example, improper fraction 

  • Not in keeping with conventional mores or good manners; indecent or immodest 

  • Not consistent with established facts; incorrect 

  • Of a complex random variable, correlated with its conjugate 

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