stiffen

verb

stiff·​en ˈsti-fən 

stiffened; stiffening ˈsti-fə-niŋ 

ˈstif-niŋ

transitive verb

: to make stiff or stiffer

intransitive verb

: to become stiff or stiffer

stiffener

ˈsti-fə-nər 

ˈstif-nər

noun

Synonyms of stiffen

• strengthen

Examples of stiffen in a Sentence

She stiffened when he grabbed her shoulder.

The dogs stiffened in alarm.

The law would stiffen penalties for tax evasion.

Recent Examples on the Web

The materials can bend, buckle, or stiffen without electronics, sensors, or active control. —Neetika Walter, Interesting Engineering, 24 Feb. 2026

The machine dryer agitates the clothing and prevents fibers from stiffening during drying, which is why clothing comes out feeling soft. —Emily Benda Gaylord, The Spruce, 23 Feb. 2026

Instead of masking smells with fragrance sprays, which can stain or stiffen sheepskin, all of our experts suggested using baking soda and cornstarch for removing odors. —Caroline Lubinsky, Martha Stewart, 21 Feb. 2026

Democrats in Congress stiffened their opposition to an appropriations bill for the Department of Homeland Security, leading to a partial government shutdown. —Jason Ma, Fortune, 21 Feb. 2026

Word History

First Known Use

15th century, in the meaning defined at transitive sense

Rhymes for stiffen

• griffon
• gryphon
• tiffin

Kids Definition

stiffen

verb

stiff·​en ˈstif-ən 

stiffened; stiffening -(ə-)niŋ 

: to make or become stiff or stiffer

stiffener

-(ə-)nər 

noun