ambush vs obstruct

ambush

verb
  • To attack by ambush; to waylay. 

  • To station in ambush with a view to surprise an enemy. 

noun
  • The act of concealing oneself and lying in wait to attack by surprise. 

  • The concealed position or state from which a surprise attack is launched. 

  • An attack launched from a concealed position. 

  • The troops posted in a concealed place, for attacking by surprise; those who lie in wait. 

obstruct

verb
  • To block or fill (a passage) with obstacles or an obstacle. See synonyms at block. 

  • To get in the way of so as to hide from sight. 

  • To impede, retard, or interfere with; hinder. 

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