Heavy Hydrogen
This page is the CodyCross answer for the clue below from Prehistory, Group 1258, Puzzle 3 (Use of Pottery).
Question is: Heavy Hydrogen
and the answer is: DEUTERIUM
Word Meaning:
DEUTERIUM — (uncountable, physics) An isotope of hydrogen with one proton and one neutron in each atom - 21H.
Definitions from Wiktionary.