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chief; main; principal; important
main secondary or supporting role (in kyogen)
「主」 has other readings with different meanings.
この製品の主な特徴は軽量で丈夫なことだ。
The main features of this product are that it's lightweight and durable.
彼女は主に海外営業を担当している。
She is mainly in charge of overseas sales.
会議の主な議題は予算配分についてだった。
The main topic of the meeting was about budget allocation.