accidentally

This adverb describes an action performed without intention or by chance. It carries a neutral to slightly negative connotation, often used to explain a mistake or an unforeseen event to mitigate blame or clarify that there was no malicious intent.

While "incidentally" is sometimes used as a synonym in very specific contexts, "accidentally" specifically denotes a lack of purpose or a failure of intent. In contrast, "by chance" often suggests a lucky or random occurrence, whereas "accidentally" frequently implies a clumsy or erroneous action.