Why is the ThreadDeath class not called ThreadDeathError instead?

Almost all Error subclasses in Java include the "-Error" suffix in their names, but not ThreadDeath. Why is this? This makes it hard to remember if it is a subclass of Error or Exception.

The javadocs for ThreadDeath say this:

An application should catch instances of this class only if it must clean up after being terminated asynchronously. If ThreadDeath is caught by a method, it is important that it be rethrown so that the thread actually dies.

and

The class ThreadDeath is specifically a subclass of Error rather than Exception, even though it is a "normal occurrence", because many applications catch all occurrences of Exception and then discard the exception.

What it is saying is that an application should treat ThreadDeath differently from both Exception and (other) Error classes.

Since the exception should be treated differently, it makes sense to use a class name that doesn't fit the normal patterns.

However, this should be of historic interest anyway. The Thread.stop() method that throws this was deprecated over 20 years ago. Your code shouldn't use stop(), and hence should not need to concern itself with this exception. And neither should you.