dumping vs unloading

dumping

noun
  • The disposal of something no longer needed, or of no value. 

  • Selling goods at less than their normal price, especially in the export market as a means of securing a monopoly. 

unloading

noun
  • The act by which something is unloaded. 

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