oak used for charcoal, (kokuji)
椚 is a Japanese-made kanji (kokuji) for a specific type of oak tree, particularly one whose wood is used for making charcoal.
椚 is a kokuji (Japanese-made character) combining 木 (tree) with 門 (gate), likely chosen for its sound くぬぎ to represent the kunugi oak. The exact historical reasoning behind the component choice is uncertain.
Picture a sturdy oak tree (木) growing beside a gate (門). The gate is made from its wood, which is also perfect for making charcoal.
For くぬぎ, imagine a cook needing oak charcoal for a barbecue: 'Cook, new gig!' — cook new gig -> くぬぎ, and the oak charcoal fuels the fire.
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