heavy hydrogen vs isotope

heavy hydrogen and isotope both are nouns.

Word	Noun	Adjective	Verb	Adverb
heavy hydrogen	Yes	No	No	No
isotope	Yes	No	No	No

As nouns, isotope is a hypernym of heavy hydrogen; that is, isotope is a word with a broader meaning than heavy hydrogen:

heavy hydrogen: an isotope of hydrogen which has one neutron (as opposed to zero neutrons in hydrogen)
isotope: one of two or more atoms with the same atomic number but with different numbers of neutrons

Other hypernyms of heavy hydrogen include hydrogen atom.

heavy hydrogen (noun)	isotope (noun)
an isotope of hydrogen which has one neutron (as opposed to zero neutrons in hydrogen)	one of two or more atoms with the same atomic number but with different numbers of neutrons