noun (n)

• the act of becoming stiff(noun.act)

  Example:
  Stiffening his shoulders, he prepared to advance.
  

  source: wordnet30
• the process of becoming stiff or rigid(noun.process)

  Synonym:
  rigidification, rigidifying
  

  source: wordnet30
• Act or process of making stiff.(noun)

  source: webster1913