The phrase "have at it" is often used to encourage someone to go ahead and do something or try their best. Antonyms, or words with opposite meanings, might include phrases such as "hold back" or "take it easy," which discourage enthusiastic action or encourage caution. Other antonyms might include phrases such as "step aside" or "stand down," which suggest staying out of the way or avoiding conflict. Alternatively, "restrain" or "limit" might be antonyms for this phrase, suggesting that someone should moderate their efforts or avoid going too far. Ultimately, the antonyms for "have at it" depend on the specific context and the desired outcome.