the.com/waistline

means The natural narrowing of the torso where your waist is, and by extension the measurement of it — the line tailors use and bodies ignore.

from Simple compound of 'waist' plus 'line,' stitched together in the 1800s by dressmakers and tailors who needed a plain word for where a garment should cinch. 'Waist' itself traces back to Old English roots tied to growth and size (related to 'wax,' as in to grow), from a time when the waist just meant the part of the body that grows — before fashion turned it into a number to argue with.