Antonyms for the word "plop down" include gently place, gingerly set, delicately drop, and gradually lower. These antonyms all suggest a slow and careful movement, as opposed to the sudden and careless action implied by "plop down." Another antonym for "plop down" would be to stand up, indicating a complete absence of sitting or dropping down. In essence, these antonyms all suggest a more deliberate and controlled action, whereas "plop down" denotes a sudden and perhaps careless movement. By choosing an antonym, one can communicate a different attitude or intention in a given situation, adding texture and nuance to one's language.