1. an art of sound in time that expresses ideas and emotions in significant forms through the elements of rhythm, melody, harmony, and color.
2. the tones or sounds employed, occurring in single line (melody) or multiple lines (harmony), and sounded or to be sounded by one or more voices or instruments, or both.
3. musical work or compositions for singing or playing.
4. the written or printed score of a musical composition.
5. such scores collectively.
6. any sweet, pleasing, or harmonious sounds or sound: the music of the waves.
7. appreciation of or responsiveness to musical sounds or harmonies: Music was in his very soul.
8. Fox Hunting. the cry of the hounds.
9. face the music, to meet, take, or accept the consequences of one's mistakes, actions, etc.: He's squandered his money and now he's got to face the music.
1200–50; ME musike < L mūsica < Gk mousik (téchnē) (the art) of the Muse, fem. of mousikós, equiv. to Moûs(a) Muse + -ikos -ic
I thought up a definition, but on review I think I'll go with the dictionary on this one. :)