jats:titleAbstract</jats:title>jats:pIn partially ordered magnets, order and disorder coexist in the same magnetic phase, distinct from both spin liquids and spin solids. Here, we determine the nature of partial magnetic ordering in the canonical frustrated antiferromagnet Gdjats:sub2</jats:sub>Tijats:sub2</jats:sub>Ojats:sub7</jats:sub>, in which Gdjats:sup3+</jats:sup> spins occupy a pyrochlore lattice. Using single-crystal neutron-diffraction measurements in applied magnetic field, magnetic symmetry analysis, inelastic neutron-scattering measurements, and spin-wave modeling, we show that its low-temperature magnetic structure involves two propagation vectors (2-jats:boldk</jats:bold> structure) with suppressed ordered magnetic moments and enhanced spin-wave fluctuations. Our experimental results are consistent with theoretical predictions of thermal fluctuation-driven order in Gdjats:sub2</jats:sub>Tijats:sub2</jats:sub>Ojats:sub7</jats:sub>, and reveal that inelastic neutron-scattering measurements on powder samples can solve the longstanding problem of distinguishing single-jats:boldk</jats:bold> and multi-jats:boldk</jats:bold> magnetic structures.</jats:p>