Used in patterns like '〜はおろか' or '〜もおろか' to mean 'not to mention' or 'needless to say', indicating that if one thing is true, then an even lesser/other thing certainly is.
漢字はおろか、平仮名もまだ全部書けない。
Not to mention kanji, I still can't write all the hiragana.
彼は毎日の掃除はおろか、部屋の片付けさえしない。
Needless to say he doesn't do daily cleaning; he doesn't even tidy his room.
英語はおろか、日本語も話せない外国人がいる。
There are foreigners who can neither English nor, let alone, Japanese.
Negligent, careless, or remiss — failing to give proper attention or care to something. (Somewhat old-fashioned/literary in this sense.)
安全対策を疎かにすると大事故につながる。
Neglecting safety measures can lead to a serious accident.
勉強を疎かにしてはいけない。
You shouldn't neglect your studies.
仕事を疎かにする態度は評価を下げる。
An attitude of neglecting your work lowers your evaluation.