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specialist; expert; professional; authority; pundit
この問題は専門家に相談した方がいい。
It would be better to consult a specialist about this problem.
専門家の意見を参考にして計画を立てた。
I made a plan using an expert's opinion as reference.
彼は長年の経験を持つ専門家として知られている。
He is known as a specialist with many years of experience.