Gerund; denotes the act or process of making someone or something more slender. Usually uncountable.
slenderizinggerundium / partizip präsens Used attributively to describe garments, activities, or effects that make someone or something appear slimmer.
She wore a slenderizing dress that made her look taller.
Она надела стройнящее платье, которое сделало её выше.
slenderizegerundium / partizip präsens Used attributively to describe something that makes a person or object appear slimmer.