Ideogrammic compound (會意): 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.
The etymological relationship between “music” and “joy” has been discussed in Wulff (1935) and Unger (1983). Unger draws comparison with the following semantic parallelism in Tibetan: རོལ་མོ(rol mo, “music”) and རོལ(rol, “to enjoy; to amuse oneself; to play”).