quadrium

noun3

1. •
   (rare) A highly unstable synthetic isotope of the element hydrogen, 41H, having one proton and three neutrons.

   • The decimal character of 4.1 is a reminder that this is not a conventional H isotope such as quadrium, ⁴H, or other isotopes up to ⁷H, with lifetimes, when known in the 0.1 to 1 zs range. — 2011
2. •
   (rare) A quadrium atom or nucleus.
3. •
   Synonym of quadrivium.

   • Church music was carefully taught at the universities. IT was of the four sciences of the quadrium, and was a means of promotion in the church and colleges. — 1861