title of a Noh play, (kokuji)
塰 is a rare kokuji (Japan-made kanji) with no clear standalone meaning. It appears as the title of a Noh play, but its meaning outside that context is uncertain.
塰 is a kokuji composed of 海 (sea) and 土 (earth), likely created to represent a concept related to the sea and land. The exact historical development is uncertain.
The top is 海 (sea) and the bottom is 土 (earth). Picture a place where the sea meets the land, perhaps a coastal setting, which fits the Noh play title.
For あま, imagine a sea diver (海女, あま) standing on the earth (土) at the shore: あま cues the reading while the components reinforce the sea-and-land image.
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