Left-side
阝 is the mound radical — the compressed left-position form of
阜, picturing a hillside with three terraced ledges (distinct from the right-side
阝 'city' in
邓,
郝). Indexes
阻 with the terrain family (
阵 array,
险 danger,
陡 steep). Carries the core meaning: an obstacle, originally a steep hill that blocks the road.
