Antineutron
An antineutron shares similar properties to that of a neutron, however its spin directly opposes that of a normal neutron.

In Spock's memory test on  in 2286,  one of the questions was: "Adjust the sine wave of this magnetic envelope so that antineutrons can pass through it but anti-gravitons cannot." ()

In 2375, Tuvok detected antineutrons in the remains of the Silver Blood . ()

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