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negligent; neglectful; careless; remiss
「疎か」 has another reading with different meanings.
健康管理を疎かにすると病気になる。
If you neglect health management, you'll get sick.
仕事が忙しくて家庭を疎かにしていた。
I was neglecting my family because work was busy.
基本を疎かにしては上達できない。
You can't improve if you neglect the basics.