Definition of neutrinoless in US English:

neutrinoless

adjective

Particle Physics
  • Designating an instance of the simultaneous beta decay of two neutrons in which the two antineutrinos predicted by theory are not observed.

Origin

1960s; earliest use found in Physical Review Letters. From neutrino + -less.

Pronunciation

neutrinoless

/njuːˈtriːnəʊləs/