steep, sloping, abruptly, sudden
陡 centers on a sharp, sudden incline or change: something steep, sloping abruptly, or happening suddenly without warning.
陡 combines ⻖ (mound, hill) with 走 (run), suggesting a hill that runs steeply upward. The exact historical development is uncertain, but the component combination fits the meaning of a steep slope.
The mound radical ⻖ on the left is a hill, and 走 on the right means run. Picture a hill so steep that you have to run just to keep your footing—it's abrupt and sloping.
For トウ, imagine a steep hill shaped like a toe: toe -> トウ, and the hill rises abruptly like a giant toe pointing upward.