愉快

 Though I knew all these colocations well before it never occurred to me there are a lot of ways to describe happy in Chinese and perhaps more, certainly by frequency, than in English
开心 - open hearted i.e. well disposed in other words happy, inner attitude
高兴 - gāoxìng excited and happy, external stimulus
快乐 - kuaile used for expressing wishes
愉快 - yúkuài joyous, relaxed, pleasant
幸福 - xìngfú happiness in ones life