element zero

Noun

1. Synonym of neutronium (“material composed of neutrons”).

   Synonyms: neutronium

   Coordinate Terms: neutron free neutron tetraneutron neutron star neutron star matter neutron-degenerate matter neutron matter neutron degeneracy n

2. Synonym of muonium.

   Synonyms: muonium

   Coordinate Terms: protium deuterium tritium hydrium hydrogen-0 hydrogen-1 hydrogen-2 hydrogen-3 hydrogen muon anti-muon muononium exotic atom atom onium meson

3. A fictional chemical element with element number/atomic number/proton number zero (0), often with unrealistic properties.
4. Used other than figuratively or idiomatically: see element, zero.