accidental
Definitions
Happening by chance, unintentionally, or unexpectedly.
Not essential or intrinsic to the nature of something; incidental.
Examples
The discovery of the new planet was entirely accidental.
He made an accidental error while typing the final report.
Synonyms
unintentional unplanned chance fortuitous inadvertent coincidental random
Antonyms
intentional deliberate planned purposeful calculated premeditated voluntary