mound, roundish mass
垚 centers on a raised pile of earth: a mound or a roundish mass of soil.
垚 is formed by tripling the earth radical 土, suggesting a large or prominent mound of earth. The exact historical development is uncertain, but the triplication pattern is a known way to intensify meaning.
Three piles of earth 土 stacked together create a noticeable mound or roundish mass.
For ギョウ, imagine a giant mound of earth shaped like a gyoza dumpling: gyo -> ギョウ, and the mound is as round as a gyoza.
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