超重氫

tritium / 3H / radioactive isotope of hydrogen having 2 neutrons in its nucleus, so atomic weight 3

to repeat / repetition / again / re- / classifier: layer

heavy / serious / to attach importance to

to exceed / to overtake / to surpass / to transcend / to pass / to cross / ultra- / super-

overweight (baggage, freight)

heavy hydrogen (isotope) / deuterium

hydrogen (chemistry)