Learner's definition of INCIDENTALLY
1 : as something that is less interesting or important
The report discusses the problem only incidentally. [=in passing]
Not incidentally, the market slump was followed by widespread layoffs.
2 — used to introduce a statement that provides added information or that mentions another subject
I recently met his wife who, incidentally [=by the way], is a well-known author.
This product is the best—and, incidentally [=by the way], the most expensive—of its kind.
Incidentally [=by the way], I saw Susan yesterday and she asked about you.