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

Not to mention their unusually flexible blood vessels could also help compensate for stiffening heart tissue. — Melissa Cristina Márquez, Forbes.com, 1 Aug. 2026

Even simple movements can encourage healthy blood flow and keep fascia from stiffening up. — Jennifer Heimlich, Time, 27 July 2026

This remains soft during low-energy movement but stiffens upon high-impact force. — Arthur Zaczkiewicz, Footwear News, 27 July 2026

Older dogs stiffen up, scratch more, lose a step, and their owners want to help. — Daniel Fusch, USA Today, 17 July 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