Definition of stiffen verb from the Oxford Advanced American Dictionary

     

    stiffen

     verb
    verb
    NAmE//ˈstɪfn//
     
    Verb Forms present simple I / you / we / they stiffen
     
    he / she / it stiffens
     
    past simple stiffened
     
    -ing form stiffening
     
     
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  1. 1[intransitive, transitive] to make yourself or part of your body firm, straight, and still, especially because you are angry or frightened stiffen (with something) She stiffened with fear. stiffen something (with something) I stiffened my back and faced him.
  2. 2[intransitive, transitive] (of part of the body) to become, or to make something become, difficult to bend or move stiffen (up) My muscles had stiffened up after the climb. stiffen something stiffened muscles
  3. 3[transitive, intransitive] stiffen (something) to make an attitude or idea stronger or more powerful; to become stronger synonym strengthen The threat of punishment has only stiffened their resolve (= made them even more determined to do something).
  4. 4 [transitive] stiffen something (with something) to make something, such as cloth, firm and unable to bend
See the Oxford Advanced Learner's Dictionary entry: stiffen