1. the process of becoming stiff or rigid
2. material used to make something stiff or firm

1. present participle of stiffen; making or becoming stiff

Examples

• The cold weather caused a stiffening of his joints.
• She added stiffening to the collar to help it hold its shape.
• The fabric stiffening made the curtains stand upright.
• His muscles were stiffening after the long workout.
• The concrete is stiffening as it begins to set.
• The tailor used interfacing as stiffening for the jacket lapels.
• We noticed a stiffening in his attitude toward the proposal.