incidentally

incidental +‎ -ly

incidentally (comparative more incidentally, superlative most incidentally)

1. (manner) In an incidental manner; not of central or critical importance.

   The book discussed the subject, but only incidentally.

   • 1951 April, D. S. Barrie, “British Railways: A Survey, 1948-1950”, in Railway Magazine, number 600, page 225:

     Not everybody welcomes standardisation as a principle, because it reduces variety (and, incidentally, tends to dispose of the quainter and more picturesque anomalies).

2. By chance; in an unplanned way.
3. (speech act, conjunctive) Parenthetically, by the way.

   Incidentally, did you hear anything new from your brother yesterday?

• (parenthetically): apropos, as a matter of fact, by the way

• (antonym(s) of “in an incidental manner”): inevitably, certainly

• coincidentally