Overhear and Eavesdrop [closed]

Solution 1:

Eavesdropping is a kind of listening (it is done secretly).

Overhearing is a kind of hearing (it is accidental, or heard over other noise, or heard though it was not supposed to be).

The essential difference is that between listening and hearing. Listening is necessarily intentional; hearing is not; etc.

Solution 2:

Overhearing has nothing to do with intention but only with whether you hear or not. On the other hand, eavesdropping has nothing to do with whether you hear or not but only with intention. So, based on that, here's my answer to your questions:

Am I right to think that overhearing is always unintentional, and eavesdropping is always intentional?

You're right as to only the second part of your question. Overhearing can be intentional or unintentional. And eavesdropping is always intentional.

Or is eavesdropping a special case of overhearing, i.e. overhearing can refer to both intentional and unintentional circumstances?

No, eavesdropping is not a special case of overhearing even though overhearing can be intentional and unintentional. For example, when you're trying to eavesdrop but fail to hear anything, you're eavesdropping but not overhearing.