Antonyms for the word "livened up" can include dull, deaden, calm, and depress. When something is dull, it lacks energy or enthusiasm, and there is no excitement or stimulation. Deaden means to reduce or eliminate sound, color, or feeling, making something feel lifeless. Calm relates to peacefulness and can imply a sense of tranquility or stillness, which can seem boring or uneventful to some. To depress is to lessen enthusiasm or vigor, perhaps leading to a sense of sadness, hopelessness, or lethargy. All of these words are the opposite of livened up, indicating a lack of energy or excitement.