Verb
To make stiff; to make less pliant or flexible; as, to stiffen cloth with starch.
To inspissate; to make more thick or viscous; as, to stiffen paste.
To make torpid; to benumb.
To become stiff or stiffer, in any sense of the adjective.
Source: Webster's dictionarytighten the rules Source: Internet
stiffen the regulations Source: Internet
Stiffen the cream by adding gelatine Source: Internet
He stiffened when he saw his boss enter the room Source: Internet
A braced monoplane wing must support itself fully, while the two wings of a biplane help to stiffen each other. Source: Internet
Although in 1979 Murray was the first to use lightweight " carbon fibre composite " panels to stiffen Brabham's aluminium alloy monocoques, he echoed his predecessor Tauranac in being the last to switch to the new fully composite monocoques. Source: Internet