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principal occupation; main job
professional; an expert; specialist
I (of a government official, etc.); me
本職はエンジニアで副業もやっている。
My main job is engineering, and I do side work too.
料理は本職ではなく趣味だ。
Cooking is just a hobby, not my profession.
本職に専念するため副業をすべてやめた。
I quit all my side jobs to focus on my main work.