The term 'Substance That Cures All Ills' can be summarized by the crossword solution 'ELIXIR' (6 letters). An ELIXIR is a magical or medicinal potion that is believed to cure all diseases and prolong life indefinitely. It has been used in many cultures throughout history, from ancient Egypt to medieval Europe. In modern times, elixirs are often used in homeopathic medicine and alternative healing practices.