masked vs skulking

masked

adj
  • Wearing a mask or masks. 

  • Concealed; hidden. 

  • Personate. 

  • Characterized by masks. 

  • Having the anterior part of the head differing decidedly in color from the rest of the plumage. 

skulking

noun
  • The action of one who skulks. 

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