What does the word harden mean?

Usage examples for harden

  1. Their bodies are covered with short soft spines, which, however, speedily harden. – Natural History of the Mammalia of India and Ceylon by Robert A. Sterndale
  2. Nay, O my children, harden not your hearts to such warfare, neither turn upon her own heart the mastering might of your country; and thou, be thou first to forgive, who drawest thy descent from heaven; cast down the weapons from thy hand, O blood of mine. – The Aeneid of Virgil by Virgil
  3. Harden comes right out in the open. – The Blot on the Kaiser's 'Scutcheon by Newell Dwight Hillis