the.com/snowball

means A compressed ball of snow, or—more commonly used in its verb form—something small that grows larger and more consequential as it rolls along, like a plan, a lie, or a debt.

from Simple and old: 'snow' plus 'ball,' describing exactly what children have packed in their mittens for centuries. The literal noun is Old English stock, but the figurative sense — an effect that compounds and accelerates, 'snowballing' out of control — is the more interesting development, emerging from the obvious physics of the thing: push a small snowball downhill and it picks up mass, speed, and momentum with every rotation. The metaphor just borrows what gravity and snowpack do for free.