point d'appui vs sprag

point d'appui

noun
  • An advantageous defensive support; a foothold. 

  • A given point or body upon which troops are formed, or by which they are marched in line or column. 

sprag

verb
  • To prop or sustain with a sprag. 

  • To check the motion of, as a carriage on a steep slope, by putting a sprag between the spokes of the wheel. 

noun
  • A billet of wood; a piece of timber, a similar solid object or constructed unit used as a prop. 

  • A young salmon. 

How often have the words point d'appui and sprag occurred in a corpus of books? (source: Google Ngram Viewer )