clod of earth, land
坴 centers on a solid mass of earth: a clod or lump of soil, and by extension the land itself.
坴 combines 土 (earth) with 圥, which likely contributes the sound. The character represents a lump or clod of earth.
The bottom 土 is earth, and the top 圥 looks like a pile of dirt. Picture a solid clod of earth sitting on the ground.
For リク, imagine a clod of earth that is so hard it feels like a brick: brick -> リク, and the clod is as solid as a brick.
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