Five readings on paper, but only two are productive:
乐 (happy) and
乐 (music). Rule of thumb: emotion words take lè (
快乐,
乐观); sound and instrument words take yuè (
音乐,
乐器). The other three are rare: surnames Lè and Yuè (different families, same written form); lào appears only in northern place names like
乐亭; classical yào means 'to take pleasure in', as in Confucius's
知者乐水 ('the wise delight in water').