definition of
stiffen

[1] #1 stiffen v. become stiff or stiffer; "He stiffened when he saw his boss enter the room". wn

[2] #2 stiffen v. make stiff or stiffer; "Stiffen the cream by adding gelatine". wn

[3] #3 stiffen v. [tighten, tighten up, constrain] restrict; "Tighten the rules"; "stiffen the regulations". wn