Acting recklessly or without consideration; done at random or haphazardly (often used as '〜に' adverbially).
闇雲に走り出してはいけない。
You mustn't run off recklessly.
彼は闇雲に投資して大損した。
He invested blindly and suffered heavy losses.
問題を闇雲に否定するのではなく、まず原因を調べよう。
Instead of dismissing the problem indiscriminately, let's first look into the cause.