Hyponeutronium
- Colloquially known as "neutronium" (TNG Novel: The Buried Age)
- Not to be confused with collapsed matter from neutron stars
- Wide class of hyper-dense alloys composed of heavy transuranic elements (TNG Novel: The Buried Age)
- Amongst the sturdiest, most durable substances known (TOS: "The Doomsday Machine"; TNG Novel: The Buried Age; TNG: "Relics"; DS9: "To the Death", "What You Leave Behind")