stiffen
stiff‧en /ˈstɪfən/
verb1. [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
stiff‧en /ˈstɪfən/
verb1. [intransitive] if you stiffen, your body suddenly becomes firm, straight, or still because you feel angry or anxious OPP relax:
2. [intransitive and transitive] to become stronger, more severe, or more determined, or to make something do this:
3. [intransitive] (also stiffen up) to become painful and difficult to move:
4. [transitive] to make material stiff so that it will not bend easily