Lucubrate means to study or work hard, especially at night. Some antonyms for this word would be "slack off," "procrastinate," or "rest." These words indicate a lack of effort or energy, and a preference for taking it easy instead. Other antonyms could include "play," "relax," or "chill," which suggest a complete break from work, study, or intellectual pursuits. These antonyms all have a lighthearted or casual tone, which is the opposite of the serious and focused approach that lucubrate implies.