adverb, adverb taking the 'to' particle, noun or participle which takes 'suru'
sneakily; secretly; stealthily
Describes doing something in a quiet, furtive manner, often to avoid being noticed. Often used with する or と. Compare こっそり, which is more about doing something quietly without being noticed, while こそこそ can imply a slightly more suspicious or guilty nuance.
See also: こっそり
彼はこそこそと部屋を出て行った。
He sneaked out of the room.
こそこそ話すのはやめてください。
Please stop whispering secretly.