helium-3

The word is a modern scientific compound. The first part, "helium," originates from the Greek 'hēlios' (sun), as the element was first detected spectroscopically in the solar corona before being found on Earth. The suffix "-ium" is a standard New Latin ending for metallic elements. The second part, "-3," is a numerical designator following the element name, a systematic nomenclature in chemistry and physics to distinguish between isotopes based on their atomic mass. Thus, "helium-3" literally means "the isotope of the element helium with a mass number of 3," a meaning that is directly and logically preserved in its modern technical usage.

Structure: helium (element) + 3 (isotope number) - helium: From the Greek 'hēlios' (sun), via New Latin. The name of the chemical element. - 3: A numeral, used here to denote the specific isotope's mass number (total protons and neutrons).