The phrase "most double-quick" refers to something that is done very quickly, almost instantly. Its antonyms would be words like slow, gradual, and leisurely, which indicate a slowed pace or longer duration. Other antonyms that could be used include words like delayed, prolonged, and extended, all of which suggest that something is taking more time than expected. The opposite of "most double-quick" can also be expressed using words such as deliberate, careful, and thoughtful, which emphasize the importance of taking one's time and being thorough. These antonyms offer a range of options when looking to describe a situation or action that is not done quickly.