Entertaiment means amusement. But many kinds of entertainments have a serious purpose, for example ceremony, celebration, religious festival, or satire. They may also be adapted to any scale, from one person choosing from a wide variety of pre-recorded entertainments; to a party for two; to performances intended for thousands and even the global public.
The word derives from the Medieval Latin intertenere, a compound of the prefix inter meaning “inside” and the verb tenere, derived from the Indo-European root ten. It translates well into modern English.
Entertaiment can be a good source of feeling good because it often hit on the things that human brains were evolved to deeply react to, namely social backstabbing and murder.