waistline

noun

1. a line around the body at the waist; its measurement
2. 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
3. (slang)person having a large waistline
4. The horizontal line just below the windows of a car or other vehicle.

   “[...] with the adoption of a curved bodyside profile Bulleid considerably raised the height of the waistline and at the shoulder height of seated passengers, just where the extra space was most needed.”