terrain vs topsoil

terrain

noun
  • The surface of the earth; the ground. 

  • A single, distinctive rock formation; an area having a preponderance of a particular rock or group of rocks. 

  • An area of land or the particular features of it. 

topsoil

verb
  • To remove the topsoil from. 

noun
  • The most fertile soil, easiest to start new plants in. 

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