1 ~ (to sth) happening in connection with sth else, but not as important as it, or not intended:
The discovery was incidental to their main research. * incidental music (= music used with a play or a film / movie to give atmosphere) * You may be able to get help with incidental expenses (= small costs that you get in connection with sth).
2 ~ to sth (technical) happening as a natural result of sth:
These risks are incidental to the work of a firefighter.
noun [usuallypl.] something that happens in connection with sth else, but is less important:
You'll need money for incidentals such as tips and taxis.
