Thin has a meaning of “not well fleshed,” but does it also carry a meaning of “being weak or feeble”? In the Merriam-Webster, it does carry a meaning of “lacking substance of strength,” but it uses “thin plot/broth” to make the example.
Is it okay to say someone is to thin to do anything which needs a lot of strength? I just find it misleading to say, because thin doesn’t always means weak. If you google, there is a title such as “Michael Jackson is too thin to play live.” Is it OK to say so? Somebody argued that it’s a euphemism to say so.
If thin were used to suggest that someone is weak, it would be a euphemism, but as far as I have seen, it is not generally used in this way. As the Merriam-Webster entry suggests, thin and weak are synonyms in reference to things such as flavors, but not in reference to physical strength. If you are looking for a word that means both “not well fleshed” and “weak or feeble,” then the word which would normally be used is scrawny.