the antiparticle of a neutron; a particle having the same mass as the neutron but a magnetic moment of opposite sign
antineutron in American English
(ˌæntaɪˈnuˌtrɑn; ˌæntiˈnuˌtrɑn; ˌæntɪˈnuˌtrɑn)
US
noun
the antiparticle of the neutron, with the same mass and spin as the neutron, but with a positive magnetic moment (the neutron has a negative magnetic moment)