1. enter- (inter-) + -tain + -ment.
2. => keep or hold someone's mind among many different and interesting things.
=> keep or hold something like amusing or treat between / among people.
=> keep or hold something attractive or interesting among / in one's mind.
3. 所谓花花世界、五彩缤纷、其乐无穷，由此引申义：娱乐，助兴。
4. 类推：The original Old French version of enterprise was emprise.
5. => The original Old French version of entertain was *emtenir(*emtain).
6. 因此这里的enter-前缀应该说还含有“in”的含义，这还可以从单词enter及该前缀的源头可以看出来。
7. enter- "in" => hold or keep one's mind in something, hold (in), keep (in), maintain (in).