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1. The act of becoming stiff
   "stiffening his shoulders, he prepared to advance"
    
2. The process of becoming stiff or rigid
   - rigidifying, rigidification

1. Become stiff or stiffer
   "He stiffened when he saw his boss enter the room"
    
2. Make stiff or stiffer
   "Stiffen the cream by adding gelatine"
    
3. Restrict
   "stiffen the regulations"
   - tighten, tighten up, constrain

Derived forms: stiffenings

See also: stiffener

Type of: action, activity, alter, bound, change, confine, limit, modify, natural action, natural process, procedure, process, restrain, restrict, throttle, trammel

Antonym: loosen

Encyclopedia: Stiffening