  We present the discovery of X-ray polarization from the neutron star low-mass
X-ray binary and Z-source, GX~340$+$0, using an Imaging X-ray Polarimetry
Explorer (IXPE) observation in March 2024. Along with the IXPE observation, we
conducted an extensive X-ray and radio monitoring campaign to ascertain the
source properties during and around the IXPE observation. The source was within
the horizontal branch throughout the multiwavelength campaign. We measured a
significant X-ray polarization in 2--8 keV with polarization degree (PD) =
$4.02 \pm 0.35$% and polarization angle (PA) = $37.6 \pm 2.5^\circ$. The
energy-dependent polarization indicates that in the 2-2.5 keV energy range, the
PA is much lower, $\sim9\pm8^\circ$, while other energy bands are consistent
with the PA found over 2.5--8 keV. The simultaneous AstroSat-IXPE
spectro-polarimetric observations provide some evidence for independent
polarization from various spectral components, hinting at a disparity in the PA
from the accretion disk and the Comptonized emission, while suggesting an
unpolarized emission from the blackbody component. Radio observations in the
0.7--9 GHz frequency range reveal a non-detection of radio emission in 0.7-1.5
GHz and a significant detection in 5.5--9 GHz, suggesting the presence of a
spectral break in 1.5-5.5 GHz. Using ATCA observation we place upper limits on
the radio polarization at $<$6% on the linear polarization and $<$4% on the
circular polarization at 3$\sigma$ level. We discuss the origin of the X-ray
polarization and its implications on the geometry of the spectral components.
