Entertaiment means having a good time, playing games and sports, watching TV, listening to music, reading books or magazines, attending concerts and other live performances, and viewing or creating visual art. It also means drama, backstabbing and murders which are themes the human brain was shaped to understand in order to function in a social world. It stimulates the brain to realease seratonin and dopamine and gives a good feeling considering we are evolved to react deeply to such things.
The suffix -ment is used in English to form nouns from verb stems (amazement, betterment, merriment), but it is also inserted into Latin words ending in –tion, as in entretenir, for which see entry 7. It is also added to nouns to form adjectives, such as entertainer, entertain.