1. To make someone happy
2. To make someone happier than his or her present condition, though not necessarily completely happy
3. To amelioriate something, to improve something
See antonym unhappienate
John was sad, but he was happienated by fucking Mary.
I saw that Joe was down in the dumps so I bought him some pot to happienate him.
My car was broken, but I happienated it by fixing the carburator.