sadist. noun. Someone who gains pleasure from inflicting pain on others.

Hehe... I know, bringing out the big, dirty guns... so yes, the word comes from sadism which is traditionally the act of gaining sexual gratification through inflicting pain and degradation on others. As such, a sadist is someone who derives such pleasure through inflicting pain on others. In a more general sense, this doesn't have to be a sexual kind of thing, and can just be someone who gets a huge kick out of extreme cruelty and such.

So sure, it's one thing to describe someone as sadistic; it is, however, a whole other kettle of fish to straight-up call someone a sadist. It's less common to hear than the adjectival form, and that little difference can tend to make for a different (maybe even stronger) impact in the end use.

During PE, that sadist Mr. Leery had us run the track all period in the rain!

Quit punching the baby, you sadist!

I can't believe it, this entire website is made up of thirteen year old sadists...

Certainly makes you feel more intellectual if you call someone this than something else like "psycho" or something, huh?

(adj. form: sadistic; adv. form: sadistically.)