乐 | yuè | lè

In Mandarin Chinese, 乐 is a character for two different words:

1. 乐 (Pinyin: yuè 🔊): n. music, tune, melody, song
2. 乐 (Pinyin: lè 🔊): adj. joyful, happy, glad, enjoyable, fun; n. happiness, joy, pleasure; v. to laugh, to smile, to enjoy, to love

乐 is a simplified form of the traditional character 樂. According to Wiktionary, 樂 is an

Ideogrammic compound: 糸 (“string”) + 木 (“wood”) — strings on a piece of wood, i.e. a wooden musical instrument. The oracle bone form shows two strings connected to the wood. In the bronze inscriptions, a 白 component was added in between the two strings, which may either represent the thumb (fiddling) or a phonetic part.

Lawrence J. Howell in his Etymological Dictionary of Han/Chinese Characters gives a different explanation:

A depiction of an oak tree with acorns (ground into powder via a lengthy grinding process). Music and enjoyment are onomatopoeic, borrowed meanings, the pronunciation of the character simulating the din of a crowd → play (an instrument); amuse oneself; pleasant; fun; happy; delightful; comfort; easy.

Compounds of 乐 (1) include

• 乐 + 队 “team” = 乐队 (yuèduì): music band
• 国 + 乐 = 国乐 (guóyuè): national music
• 俗 “common” + 乐 = 俗乐 (súyuè): folk music
• 西 + 乐 = 西乐 (xīyuè): Western music

And those of 乐 (2):

• 乐 + 土 = 乐土 (lètǔ): land of happiness; paradise
• 乐 + 子 = 乐子 (lèzi): a little fun; a good time
• 快 + 乐 = 快乐 (kuàilè 🔊): happy; joyful; cheerful

One of the meaning of 快 is “happy”, so 快乐 is like “happy happy”. In its turn, 快乐 is a part of many “happy” wishes such as

• 生 + 日 + 快乐 = 生日快乐 (shēngrì kuàilè 🔊): Happy Birthday!
• 新 + 年 + 快乐 = 新年快乐 (xīnnián kuàilè): Happy New Year!
• 春 + 节 + 快乐 = 春节快乐 (chūnjié kuàilè): Happy Spring Festival, Happy Chinese New Year

In Japanese, a simplified (shinjitai) form of 樂 is used, viz. 楽. Similar to Chinese, 楽 corresponds to two different words:

1. がく (gaku): n. music
2. らく (raku): adj. comfortable, easy, simple; n. comfort, ease, enjoyment, simplicity

楽書の 壁をあはれむ 今朝の雪 蕪村 Rakugaki no kabe wo awaremu kesa no yuki The scribbling on the wall, — It looks pitiful, This morn of snow. Buson (Translated by R.H. Blyth)

Here, 楽書, literally “writing for fun”, is an alternative way to spell 落書き / らくがき (rakugaki 🔊), “doodle”, “graffiti”, “scrawl”, “scribble”, etc.

More photos related to music, happiness, hanzi and calligraphy @ Shutterstock.