"Sit still" is a phrase commonly used to instruct someone to remain in a seated position without moving. However, there are numerous synonyms that can be applied to convey the same meaning. Instead of instructing someone to "sit still", you could use alternatives such as "stay put", "remain seated", "keep yourself planted" or "maintain your position". These synonyms not only provide a variety of ways to express the idea but also add a touch of creativity and engagement to the language used. Whether you choose to utilize traditional or more innovative alternatives, the goal remains to ensure a person refrains from moving while seated.