Without intention; in an unintentional manner:
— She hit him unintentionally.

synoniem: accidentally.

Roget 621: randomly, by chance, fortuitously; unpredictably, unforeseeably; casually etc. 156; unintentionally etc. adj.; unwittingly.    en passant [Fr.], by the way, incidentally; as it may happen; at random, at a venture, at haphazard.    ... meer laten zien