causal vs indirect

causal

noun
  • a word (such as because) that expresses a reason or a cause 

adj
  • of, relating to, or being a cause of something; causing 

indirect

noun
  • An indirect cost. 

  • An indirect radiator 

verb
  • To access by means of indirection; to dereference. 

adj
  • Not of obvious or immediate cause, but as a secondary result 

  • Not focused straight at the target or subject, but by more subtle means 

  • Not involving the quickest, shortest, or most convenient path 

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