antiparticle

https://doi.org/10.1351/goldbook.A00401
Of a given particle, a particle with the same rest mass, where the two can annihilate.
Source:
PAC, 1982, 54, 1533. 'Glossary of terms used in nuclear analytical chemistry (Provisional)' on page 1535 (https://doi.org/10.1351/pac198254081533)