the world > space > extension in space > measurable spatial extent > vertical extent > extension downwards or depth > [adjective] > of specific depth (12)
Having a (specified) dimension downward.
So deep as to reach to the knee. Said of water, snow, mud, grass, etc.; also of the ground submerged or covered by these.
(a) adj. that reaches to or covers the ankles; (b) adv. so as to reach or cover the height of the ankles.
deep enough to cover a person's shoes.