The two crossword solutions for the term 'Helium or Hydrogen' are ELEMENT (7 letters) and GAS (3 letters). Helium and hydrogen are both chemical elements that exist in nature. They are both colorless, odorless, and tasteless gases at standard temperature and pressure. Helium is the second most abundant ELEMENT in the universe, while hydrogen is the most abundant. Both elements are used in a variety of applications, including rocket fuel, welding, and medical imaging.