for no particular reason; somehow or other; without thinking
Expresses doing something without a clear reason or intention, often with a nuance of absent-mindedness or vague impulse.
I looked up at the sky for no particular reason.
Somehow or other, I found myself thinking about him.
Variant using 無し; less common but seen.
Combination of 何 (what) + と (quotative) + は (topic) + なし (without) + に (adverbial). Literally 'without there being a what', i.e., without a particular reason.