Jazziness is a noun that describes a lively, upbeat, and energetic vibe or feeling. When looking for antonyms, we need to focus on words that represent a lack of energy or excitement. Some possible antonyms for jazziness could include drowsiness, lethargy, sluggishness, torpor, weariness, apathy, and ennui. These words suggest a sense of boredom, depression, or fatigue that is the opposite of the lively and stimulating mood conveyed by jazziness. Other words that could be considered include dullness, monotony, inactivity, and slothfulness. By using these antonyms, we can highlight the contrast between the dynamic and engaging nature of jazziness and the less desirable qualities that it stands in opposition to.