Accidental and incidental look similar, but they are not interchangeable.
Accidental means something was not planned, not deliberate, or unintended. It focuses on how something happened. If you say, The spill was accidental, you mean no one meant to cause it.
Incidental means something is secondary, minor, or connected to something more important. It focuses on importance or relationship, not intent. If you say, The trip caused incidental expenses, you mean the extra costs came along with the trip but were not the main point.
- Use accidental for mistakes, unintended actions, or events without intent.
- Use incidental for side effects, extra details, or things that accompany something larger.
A simple way to remember it is this: accidental is about not meaning to, while incidental is about not being central.
Compare these: Her deletion of the file was accidental. The file cleanup revealed incidental errors. The first sentence is about intent. The second is about secondary findings.