1. harsh discordance of sound; dissonance: a cacophony of hoots, cackles, and wails.
2. a discordant and meaningless mixture of sounds: the cacophony produced by city traffic at midday.
3. Music. frequent use of discords of a harshness and relationship difficult to understand.
I’d like to add another definition:
4. The sound a flock of chickens make early in the morning when they sense a predator, whether real or perceived.