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base (of a plant, tree, pillar, etc.); (part near the) root; roots (of one's hair)
root (e.g. of a problem); source
大木の根元に小さなきのこが生えていた。
Small mushrooms were growing at the base of a large tree.
歯の根元が痛むので歯医者に行くことにした。
The base of my tooth hurts, so I decided to go to the dentist.
柱の根元が腐食して建物が傾きかけていた。
The base of the pillar had corroded, and the building was starting to lean.