Synonyms of stiffen

stiffen

verb

ˈsti-fən 

as in to strengthen

to make more harsh, uncompromising, or severe

plans to further stiffen the already onerous requirements for admission to the elite military unit

Synonyms & Similar Words

• strengthen
• harden
• toughen
• harshen

Antonyms & Near Antonyms

• ease
• lessen
• soften
• ameliorate
• moderate

Example Sentences

Recent Examples of stiffen

If the washer cannot rinse all of it away, the residue can stiffen the fibers and attract additional soil. — Ashlyn Needham, Southern Living, 24 Oct. 2026

The Smart Go's polyurethane airbag uses a patented diaphragm technology and a layered internal structure to stiffen up when it's deployed. — New Atlas, 22 Oct. 2026

Davidsen bucks up her balky husband with a bloodthirsty holler, stiffens her voice against doubt, and, in her final sleepwalking scene, taps into the tender stratum of Lady Macbeth’s subconscious. — Justin Davidson, Vulture, 23 Sep. 2026

The Chiefs’ defense stiffened and Indy faced a fourth-and-8 from the 15-yard line. — Pete Grathoff, Kansas City Star, 21 Sep. 2026