Finding synonyms for the word "healthless" could be a challenging task, but there are several words that could fit the bill. Firstly, "unhealthy" could be used as a synonym, as it implies a state of being without good health or wellbeing. Secondly, "ailing" could describe someone who is not in good health or is experiencing illness or weakness. Thirdly, "unsound" could describe a person's physical or mental state as being unreliable or unstable. Fourthly, "sickly" could also be used, as it denotes someone who is weak or in poor health, often because of a chronic medical condition. Lastly, "unfit" could describe a person who is not in good physical shape or is unwell.