penny whistle vs sough

penny whistle

noun
  • A tin whistle. 

sough

noun
  • A murmuring sound; rushing, rustling, or whistling sound. 

  • A gentle breeze; a waft; a breath. 

  • A (deep) sigh. 

  • A small drain; an adit. 

verb
  • To make a soft rustling or murmuring sound. 

  • To drain. 

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