The term "stick-in-the-mud" refers to a person who is slow to change or adapt to new situations. The antonyms for this word would be flexible, adaptable, open-minded, innovative, and dynamic. A flexible person can easily adjust to different situations or circumstances, while an adaptable person can quickly change their behavior or approach as needed. An open-minded person is receptive to new ideas or perspectives, while an innovative person is creative and forward-thinking. A dynamic person is capable of handling challenges and adapting to changes with ease. These antonyms provide a positive description of people who are not stuck in their ways and can easily adapt to the changing world.