steep bank, declivity
陁 centers on a steep downward slope or bank, emphasizing the sharpness of the incline.
陁 combines the hill radical ⻖ with 㐌, which likely contributes the sound. The hill radical suggests a steep terrain feature.
The left side ⻖ is a hill, and the right side 㐌 looks like a person sliding down a steep slope. Picture a steep bank where the ground drops sharply.
For タ, imagine standing at the top of a steep bank and saying 'ta!' as you slide down: ta -> タ.