快乐(kuài lè) - happy, joyful in Mandarin

快乐 means happy or joyful. 快 (kuài) here means pleased (忄 'heart' radical with phonetic 夬). 乐 (lè) means joy; the traditional 樂 is a pictograph of a wooden frame strung for music, hence joy.

Origin

compound

Root

快 (kuài, pleased) + 乐 (lè, joy)