Accidental
Fortuitous
Synonyms: Fortuitous, occurring by chance/accident, fluky, casual, random, unexpected, unanticipated, unintentional, inadvertent, unplanned, unthinking, unwitting, unconscious, mistaken, chance, adventitious, coincidental, serendipitous, aleatory, unforeseen, unlooked-for, unintended, involuntary, unpremeditated, unmeant, unknowing, subconscious, and misguided.
Incidental
Synonyms: Incidental, by the way, supplementary, subordinate, marginal, lesser, peripheral, extraneous, parenthetical, immaterial, of little account, non-essential, unimportant, by the by, subsidiary, secondary, minor, accessory, tangential, extrinsic, irrelevant, beside the point, unnecessary, and inessential.
Example Sentences
The damage was purely accidental.
He gave her an accidental push.
She made an accidental discovery in the lab.
The fire started from an accidental spark.
His comment was accidental, not intentional.
They met through an accidental encounter.
The injury was accidental and unplanned.
That was an accidental click on the link.
He caused an accidental spill in the kitchen.
The mistake was completely accidental.