stiffen

verbs

become stiff or stiffer
"He stiffened when he saw his boss enter the room"
is derived from
antonym
is a type of (narrower)
undergo a change; become different in essence; losing one's or its original nature
"She changed completely as she grew older"; "The weather changed last night"
make stiff or stiffer
"Stiffen the cream by adding gelatine"
is derived from
is derived from
antonym
is a type of (narrower)
cause to change; make different; cause a transformation
"The advent of the automobile may have altered the growth pattern of the city"; "The discussion has changed my thinking about the issue"
causes
become stiff or stiffer
"He stiffened when he saw his boss enter the room"
restrict
"Tighten the rules"; "stiffen the regulations"