  Mutual interactions in many-body systems bring about a variety of exotic
phases, among which liquid-like states failing to order due to frustration are
of keen interest. Recently, an organic system with an anisotropic triangular
lattice of molecular dimers has been suggested to host a dipole liquid arising
from intradimer charge-imbalance instability, possibly offering an
unprecedented stage for the spin degrees of freedom. Here we show that an
extraordinary unordered(unfrozen) spin state having soft-matter-like
spatiotemporal characteristics is substantiated in this system. $^1$H NMR
spectra and magnetization measurements indicate that gigantic, staggered
moments are non-linearly and inhomogeneously induced by magnetic field whereas
the moments vanish in the zero-field limit. The analysis of the NMR relaxation
rate signifies that the moments fluctuate at a characteristic frequency slowing
down to below MHz at low temperatures. The inhomogeneity, local correlation,
and slow dynamics indicative of middle-scale dynamical correlation length
suggest a novel frustration-driven spin clusterization.
