waistline /ˈweɪstˌlaɪn/ noun4 •a line around the body at the waist; its measurement •the narrowest part of a garment, usually at the waist, but may be above or below depending on the dictates of fashion or the whim of the designer •The horizontal line just below the windows of a car or other vehicle. •(slang) person having a large waistline formswaistlines