stiffen

1. (transitive) To make stiff.Examples: "Criminal prosecutions of abusers are generally the responsibility of local authorities, but the act stiffened sentences for stalking under federal law."; "It followed a sequence of functions: a machine cuts cloth panels to be sewn, the panels are drenched with the polymer and stiffened, a robotic arm uses suction cups to lift each panel and position it in a sewing machine. Finally, the robotic arm lifts the stitched T-shirt off the sewing machine. […] The system could work for most fabrics, with the exception of leather and waterproof materials that can't be drenched with the stiffening polymer. […] Zornow has patents pending in 10 countries for the process to stiffen fabric."transitive

2. (intransitive) To become stiff.Examples: "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."intransitive