stiffen

American  

[stif-uhn] / ˈstɪf ən /

verb (used with object)

1. to make stiff.

---

verb (used without object)

1. to become stiff.

2. to become suddenly tense, rigid, or taut, as in bracing oneself for or drawing back from shock, fear, or displeasure.

   He stiffened, expecting to hear the worst.

stiffen British  

/ ˈstɪfən /

verb

1. to make or become stiff or stiffer

2. (intr) to become suddenly tense or unyielding

---

Other Word Forms

• overstiffen verb
• stiffener noun
• unstiffened adjective

Etymology

Origin of stiffen

First recorded in 1490–1500; stiff + -en ¹

Explanation

To stiffen is to become stiff or unbending. If your legs stiffen during a long plane flight, you'll want to stretch them out once you land. You can stiffen something deliberately, like when you stiffen a package with cardboard to protect it in the mail. You can also stiffen in reaction to something: "The spooky creaking sounds upstairs made us stiffen in terror." The earliest sense of this verb was "make steadfast," from a now-obsolete meaning of stiff, "gain strength."

Example Sentences

She has also vowed to stiffen prison sentences and to impose a state of emergency in areas worst hit by crime.

From Barron's • Feb. 1, 2026

This involves the buildup of dense, fibrous tissue around the tumor, made up of cells and proteins that stiffen and inflame the area.

From Science Daily • Jan. 30, 2026

Nonetheless, this is an important move that can help stiffen the spines at other schools.

From Salon • Apr. 16, 2025

Now, after shocking France at Twickenham a fortnight ago, they have found a happy habit of finding a way to win as the match teeters, nerves strain and muscles stiffen.

From BBC • Feb. 22, 2025

Ray reaches over and half hugs me, but I stiffen, so he knocks me gently on the head with his fist.

From "The Tenth Mistake of Hank Hooperman" by Gennifer Choldenko

Related Words

• reinforce
• solidify
• stabilize
• strengthen