indiscriminately; without distinction; heedless of
Used when someone acts without considering differences, boundaries, or consequences. Often followed by verbs like 使う, 食べる, 信じる, or 攻撃する.
He spends money indiscriminately.
I was so hungry that I ate everything without thinking.
手当たり次第 means 'using anything one can lay hands on' or 'indiscriminately', focusing on grabbing or using whatever is available. 見境なしに is broader and can apply to actions like believing, spending, or attacking without distinction.
From 見境 (みさかい, 'distinction' or 'discernment') + なし (without) + に (adverbial particle). The phrase literally means 'without making distinctions'.