1. to make or become rigid, hard, or less flexible
2. to become tense or rigid in posture or manner
3. to make more severe, strict, or determined

Examples

• The cold weather caused the fabric to stiffen.
• She stiffened when she heard footsteps behind her.
• Add cornstarch to stiffen the mixture.
• His back stiffened from sitting too long.
• The government decided to stiffen penalties for drunk driving.
• Her resolve stiffened after hearing the criticism.
• The glue will stiffen as it dries.