The phrase "on limb" typically means to be in a precarious or risky situation. Antonyms for this phrase would be words that suggest stability or safety. Some possible antonyms could include "secure," "stable," "balanced," "safe," "grounded," "anchored," "supported," "fixed," "settled," or "rooted." These words imply a sense of certainty and safety, as opposed to being in a risky or uncertain position. When describing a person or situation, using the right antonym can help create a clear and vivid image for the reader, and convey important information about the state of the subject.