We don't have synonyms for anti-particle yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are antiparticle and antipartticle.
(n) :
Alternative form of antiparticle. [(particle physics) A subatomic particle corresponding to another particle with the same mass, spin and mean lifetime but with charge, parity, strangeness and other quantum numbers flipped in sign; a particle that has a reversed world line to another.]
(n) :
Alternative form of antiparticle. [(particle physics) A subatomic particle corresponding to another particle with the same mass, spin and mean lifetime but with charge, parity, strangeness and other quantum numbers flipped in sign; a particle that has a reversed world line to another.]