Corporal means "of the body." Corporal punishment involves physically harming someone. A corporal is also a noncommissioned officer in the Army, Air Force, and Marines.
In the military, a corporal is a soldier who rose through the ranks as an enlisted soldier, not going to one of the military colleges. Elsewhere, this word has to do with physical things and beings. A ghost is not corporal — it has no body. In a horror movie, corporal monsters like zombies and vampires can do more damage. You can also talk about corporal pleasures, like eating and drinking. When you see the word corporal (or corporeal), think body.