sacred Shinto tree, (kokuji)
榊 refers specifically to the sakaki tree, an evergreen sacred in Shinto ritual. It is a kokuji created in Japan for this culturally important tree.
榊 is a Japanese kokuji, combining 木 (tree) with 神 (god, spirit) to denote the sacred sakaki tree used in Shinto offerings.
A tree 木 that is associated with the gods 神: the sakaki tree is the sacred tree of Shinto.
For さかき, imagine a sacred tree that prospers (sakaeru 栄える) and is pure (kiyoi 清い): saka-ki -> さかき.
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