Nouns

(n)stiffnessthe physical property of being inflexible and hard to bend
(n)stiffnessthe property of moving with pain or difficulty“he awoke with a painful stiffness in his neck”
(n)stiffnessfirm resoluteness in purpose or opinion or action“a charming host without any touch of stiffness or pomposity”
(n)awkwardness, clumsiness, gracelessness, stiffnessthe inelegance of someone stiff and unrelaxed (as by embarrassment)
(n)severity, severeness, harshness, rigor, rigour, rigorousness, rigourousness, inclemency, hardness, stiffnessexcessive sternness“severity of character”, “the harshness of his punishment was inhuman”, “the rigors of boot camp”