1) Elementary particle 2) Fundamental particle 3) Subatomic particle 4) The antiparticle of a quark 
(from the article `subatomic particle`) The baryons and mesons are complex subatomic particles built from more-elementary objects, the quarks. Six types of quark, together with their ... ...particles; that is, they have no apparent structure and cannot be resolved into something smaller. In addition, however, quarks always seem to ... ...
The anti-matter partner of the quark.
The antiparticle of a quark. 
[n] - the antiparticle of a quark
The antiparticle of a quark. See also: Antimatter, Antiparticle, Quark.
noun the antiparticle of a quark
the antiparticle of a quark.