There are several synonyms for the phrase "sit down." One of them is "take a seat," which is often used in formal settings such as meetings or at a theater. Another popular synonym is "relax," which implies a more casual or informal setting. "Settle in" is another synonym that suggests making oneself comfortable. "Park it" is a common slang phrase that is used to convey a sense of urgency or directness. Finally, "rest" or "repose" may be used to convey a sense of relaxation or recovery. Regardless of the synonym used, the goal remains the same: to take a load off and find a comfortable position.