icon vs pictograph

icon

noun
  • A small picture that represents something. 

  • A person or thing that is the best example of a certain profession or some doing. 

  • An image, symbol, picture, or other representation usually as an object of religious devotion. 

  • A type of religious painting portraying a saint or scene from Scripture, often done on wooden panels. 

  • A word, character, or sign whose form reflects and is determined by the referent; onomatopoeic words are necessarily all icons. 

pictograph

noun
  • A picture that represents a word or an idea. 

  • A graphic character. 

  • A graph that represents numerical data using pictures. 

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