hydrogen
Pronunciation: /ˈhʌɪdrədʒ(ə)n/
noun
- Hydrogen is the lightest of the chemical elements and has the simplest atomic structure, a single electron orbiting a nucleus consisting of a single proton. It is by far the commonest element in the universe, although not on the earth, where it occurs chiefly combined with oxygen as water

Origin:
late 18th century: coined in French from Greek hudro- 'water' + -genēs (see -gen)