serenade vs set one’s cap

serenade

noun
  • A love song that is sung directly to one's love interest, especially one performed below the window of a loved one in the evening. 

  • An instrumental composition in several movements. 

verb
  • To sing or play a serenade for (someone). 

set one’s cap

How often have the words serenade and set one’s cap occurred in a corpus of books? (source: Google Ngram Viewer )