stiff ‧ en /ˈstɪf ə n/ BrE AmE verb
[ Word Family: noun : ↑ stiffness , ↑ stiff ; adverb : ↑ stiff , ↑ stiffly ; verb : ↑ stiffen ; adjective : ↑ stiff ]
1 . [intransitive] if you stiffen, your body suddenly becomes firm, straight, or still because you feel angry or anxious OPP relax :
He touched her, and she stiffened.
2 . [intransitive and transitive] to become stronger, more severe, or more determined, or to make something do this:
a campaign to stiffen rules against drink-driving
Their opposition only stiffened my resolve.
3 . [intransitive] ( also stiffen up ) to become painful and difficult to move:
His joints had stiffened.
My back had stiffened up.
4 . [transitive] to make material stiff so that it will not bend easily