How to sign: any of the more than 100 known substances (of which 92 occur naturally) that cannot be separated into simpler substances and that singly or in combination constitute all matter
Similiar / Same: element
Within this category: actinium, allotrope, argon, arsenic, astatine, boron, bromine, carbon, chlorine, fluorine, germanium, helium, hydrogen, iodine, krypton, lawrencium, mendelevium, metallic element, neon, nitrogen, nobelium, noble gas, nonmetal, oxygen, phosphorus, plutonium, radon, rutherfordium, selenium, silicon, sulfur, tellurium, trace element, transactinide, transuranic element, unnilhexium, unnilquintium, unnilseptium, xenon