adverb
1.
by chance
in this discussion grave questions were brought up incidentally
Synonyms: accidentally, casually, fortuitously
Antonyms: deliberately
2.
by way of interjection or digression
another leading industry, incidentally, has quadrupled its business in four years
Synonyms: by the bye, by the way, in passing, obiter, parenthetically
Idioms: in the bygoing