An antilepton is an antimatter counterpart of a lepton. Antileptons interfer with subspace communications.
In 2369, Gul Jasad flooded subspace with antilepton interference near Deep Space 9 in order to halt its subspace communications with Starfleet while he was attempting to gain answers to his questions about the sudden disappearance of Gul Dukat's starship. (DS9: "Emissary")
External links 
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- Antilepton at Memory Beta, the wiki for licensed Star Trek works
- Antilepton at Wikipedia