Synonyms for Incidentally:

adv.

by chance (adverb)
by the bye, as a by-product, subordinately, by the way, accidentally, in passing, parenthetically.
circumstantially (adverb)
eventually, Inferentially, presumptively, uncertainly, occasionally, indirectly, inconclusively, circumstantially.

adv

by the way (adverb)
parenthetically, by the bye, speaking of, in passing.
circumstantially (adverb)
eventually, Inferentially, presumptively, uncertainly, occasionally, indirectly, inconclusively, circumstantially.

n.

coincidental, accidental, instinctive, impromptu, arbitrary, by accident, random, involuntary, unintended, spontaneous. anyway, the fact that, namely, not to mention, in any case, furthermore, even so, anyhow. by the way (noun)
parenthetically, as a side effect, speaking of, in an incidental manner, apropos of, in passing, concomitant to, as a by-product, subordinately.
incidentally (noun)
apropos, by the bye, by chance, by the way, accidentally.

Other synonyms:

furthermore, anyhow, namely, anyway. Other relevant words:
apropos, involuntary, accidentally, anyhow, accidental, in passing, by accident, namely, by chance, instinctive, by the way, speaking of, apropos of, spontaneous, furthermore, by the bye, coincidental, parenthetically, random, impromptu, unintended, anyway, subordinately, arbitrary.

Usage examples for incidentally

  1. The puzzle is to show how he did it and, incidentally to discover which prisoner was so stupidly obstinate. – Amusements in Mathematics by Henry Ernest Dudeney
  2. Hence foods not only give the body the power to do work, but incidentally they heat the body. – School and Home Cooking by Carlotta C. Greer
  3. He had, incidentally no interest on his own account in Rose Midgett- he scarcely knew her by sight- but it was pleasant to think that she would be no longer worried. – The Prelude to Adventure by Hugh Walpole