What is the meaning of stiffening?

noun

• The act of becoming stiff.
  • usage: "stiffening his shoulders, he prepared to advance"
• The process of becoming stiff or rigid.
  • synonyms: rigidifying, rigidification

verb

• Become stiff or stiffer.
  • usage: "He stiffened when he saw his boss enter the room"
  • synonyms: stiffen
• Make stiff or stiffer.
  • usage: "Stiffen the cream by adding gelatine"
  • synonyms: stiffen
• Restrict.
  • usage: "Tighten the rules"; "stiffen the regulations"
  • synonyms: stiffen, tighten, tighten up, constrain