introduce vs spearhead

introduce

verb
  • To bring (something) into practice. 

  • To cause (someone) to be acquainted (with someone else). 

  • To add (something) to a system, a mixture, or a container. 

  • To make (something or someone) known by formal announcement or recommendation. 

spearhead

verb
  • To drive or campaign ardently for, as an effort, project, etc. 

noun
  • The leading military unit in an attack. 

  • One who leads or initiates an activity (such as an attack or a campaign). 

  • The pointed head, or end, of a spear. 

  • A player who initiates attacking moves. 

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