Answer: stiffens

AnswerCrossword Clue
STIFFENSSets
STIFFENSBecomes taut
stiffensMake or become stronger or more steadfast
stiffensMake or become stiff or rigid
stiffensSTIFFEN, to make stiff (not easily bent)
stiffensSupport or strengthen (a garment or fabric), typically by adding tape or an adhesive layer