Mellifluousness is a quality that refers to sweet-sounding or pleasant to the ear. Some antonyms for this word include harshness, discordance, inharmoniousness, dissonance, stridence, and cacophony. These words are used to describe a sound that is unpleasant, jarring, or grating to the ear. For example, a screeching sound may be described as harsh, while a clashing sound may be described as discordant. It is important to note that the antonyms for mellifluousness are not necessarily negative, as there may be instances where a particular sound or tone is intended to be harsh or dissonant for artistic purposes.