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

Older dogs stiffen up, scratch more, lose a step, and their owners want to help. — Daniel Fusch, USA Today, 17 July 2026

Graham's aorta, at 71, tore, a dissection along a wall stiffened by decades of what the medical examiner called arteriosclerotic cardiovascular disease. — Dr. Céline Gounder, CBS News, 13 July 2026

Group 1 is pulmonary arterial hypertension, a rare and severe version that occurs when blood vessels in the lungs narrow and stiffen. — Elizabeth Cooney, STAT, 26 June 2026

Pulisic played a dynamic first half in the Americans' historic 4-1 victory over Paraguay to open their home World Cup nearly two weeks ago, but the AC Milan midfielder came off at halftime after an injury from training stiffened up. — ABC News, 24 June 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