Gambling is a sin. LoL
Anyway, since you already cited the definition of gambling. That is an endlessly entertainment for us gamblers, I consider it also a sin. A sin in my profession. Because in my profession, gambling or any activities that relate in gambling will revoke our license. Since it was indicated in our Code of Ethics.

Anyway, I am not yet a public servant and I am not really a gambler in physical casino. So, I am still excuse in that rule though maybe, I will teach someday and I think I should stop gambling when time comes.