type of oak, stable, (kokuji)
杤 is a kokuji (Japan-made kanji) that refers to a type of oak tree, specifically the Japanese horse-chestnut (tochi). The meaning centers on this particular tree and its wood, which is stable and useful.
杤 is a kokuji created in Japan by combining 木 (tree) with 万 (ten thousand), possibly suggesting a tree that produces many nuts or is very useful. The exact historical reasoning is uncertain.
A tree (木) that yields ten thousand (万) nuts: the Japanese horse-chestnut, a stable and productive oak.
For とち, imagine a tochi tree with a touch of stability: 'tochi' sounds like 'touch', and this oak is stable to the touch.
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