means Close-fitting stretchy garments that cover the legs, worn snug from waist to ankle as casual wear, athletic gear, or under other clothes.

from From "leg" plus the "-ing" suffix that turns a body part into the thing that covers it — the same logic that gives us "stockings." The word originally named separate protective leg coverings, often of leather or thick cloth, that travelers, soldiers, and laborers strapped on against cold, mud, and brambles. "Leg" itself is an old Norse import (leggr), nudging aside a homegrown Old English word. Only much later did the term stretch — literally — to cover today's elastic second skin.