- 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[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[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 [transitive] stiffen something (with something) to make something, such as cloth, firm and unable to bend
NAmE//ˈstɪfn//Verb Forms present simple I / you / we / they stiffen
he / she / it stiffens
past simple stiffened
-ing form stiffening