stiffen

[stif-uhn] / ˈstɪf ən /

VERB

make or become harder

Synonyms

STRONGEST

reinforce solidify stabilize strengthen

STRONG

anneal benumb brace cake candy cement chill clot coagulate condense congeal crystallize curdle firm fix freeze gel harden inflate inspissate jell jelly ossify petrify precipitate prop set starch steady tauten tense thicken

Antonyms

STRONGEST

weaken

STRONG

dilute dissolve heat liquefy melt separate soften thin unfix

WEAK

loosen

Example Sentences

Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.

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 leads them to weaken and stiffen over time and usually affects how you walk, talk, eat and breathe.

From BBC • Aug. 19, 2025

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

From Salon • Apr. 16, 2025

Traditionally, the way to stiffen a polymer network is to add more crosslinks.

From Science Daily • Nov. 27, 2024

I felt her stiffen away when 1 touched her.

From "A Farewell To Arms" by Ernest Hemingway