v. 25B6; verb
stir until the mixture stiffens : BECOME STIFF, thicken; set, become solid, solidify, harden, gel, congeal, coagulate, clot.
she stiffened her muscles 007C; without exercise, joints will stiffen : MAKE/BECOME STIFF, tense (up), tighten, tauten.
intimidation stiffened their resolve : STRENGTHEN, harden, toughen, fortify, reinforce, give a boost to.
soften, liquefy, relax, weaken.