What does the word staple mean?

Usage examples for staple

  1. No child, as a rule, can live, or, if he live, can be healthy, unless milk be the staple article of his diet. – Advice to a Mother on the Management of her Children by Pye Henry Chavasse
  2. Is the staple produce of the Russian Empire to lose its market as contraband of war? – History of Modern Europe 1792-1878 by C. A. Fyffe