something that comes with something else, but is less important than it
sometimes in a specialized sense, including:
incidental expenses or when in context, just incidentals — minor expenses not budgeted or not specified
incidental music — music in a play, television program, radio program, video game or some other form not primarily musical. (The term is less frequently applied to film music, with such music being referred to instead as the film score or soundtrack.)
Sky noises and the abrupt light told her details of careers, incidental wisdom, allowing her to risk everything because the thunder would warn her along with the snake of lighming.
There are no more uses of "incidental" in Running in the Family.