island
陦 centers on an island, a piece of land surrounded by water.
陦 combines ⻖ (hill, mound) with 寿, which likely contributes the sound. The hill radical suggests a raised piece of land, fitting the island meaning.
A hill (⻖) that stands alone in the sea, like a long-lived (寿) mound of earth, is an island.
For トウ, imagine a toe-shaped island: toe -> トウ, and the hill (⻖) on the island looks like a big toe sticking out of the water.