stiffen

verb

1. (transitive)To make stiff.

   “As Willis spoke and tried to smile the voices inside him rang together like a bell, stiffening him and hollowing him and emptying him of his troubled song.”

   “Criminal prosecutions of abusers are generally the responsibility of local authorities, but the act stiffened sentences for stalking under federal law.”

2. (intransitive)To become stiff.

   “Bewildered by the unexpected greeting, my son stiffened, but managed a polite answer.”

   “He does note that fascia, like most connective tissue in the body, stiffens with age, overuse and injury.”