To make stiff; to make less pliant or flexible; as, to stiffen cloth with starch. He stiffened his neck and hardened his heart from turning to the Lord God of Israel. 2 Chronicles 36:13. Stiffen the sinews; summon up the blood.

To make torpid; as stiffening grief.

To inspissate; to make more thick or viscous; as, to stiffen paste.

To become stiff; to become more rigid or less flexible. --Like bristles rose my stiffning hair.

To become more thick, or less soft; to be inspissated; to approach to hardness; as, melted substances stiffen as they cool. The tender soil then stiffning by degrees-- .

To become less susceptible of impression; to become less susceptible of impression; to become less tender or yielding; to grow more obstinate. Some souls, we see, grow hard and stiffen with adversity.