  A rare class of supernovae (SNe) is characterized by strong interaction
between the ejecta and several solar masses of circumstellar matter (CSM) as
evidenced by strong Balmer-line emission. Within the first few weeks after the
explosion, they may display spectral features similar to overluminous Type Ia
SNe, while at later phase their observation properties exhibit remarkable
similarities with some extreme case of Type IIn SNe that show strong Balmer
lines years after the explosion. We present polarimetric observations of
SN2018evt obtained by the ESO Very Large Telescope from 172 to 219 days after
the estimated time of peak luminosity to study the geometry of the CSM. The
nonzero continuum polarization decreases over time, suggesting that the mass
loss of the progenitor star is aspherical. The prominent H$\alpha$ emission can
be decomposed into a broad, time-evolving component and an intermediate-width,
static component. The former shows polarized signals, and it is likely to arise
from a cold dense shell (CDS) within the region between the forward and reverse
shocks. The latter is significantly unpolarized, and it is likely to arise from
shocked, fragmented gas clouds in the H-rich CSM. We infer that SN2018evt
exploded inside a massive and aspherical circumstellar cloud. The symmetry axes
of the CSM and the SN appear to be similar. SN\,2018evt shows observational
properties common to events that display strong interaction between the ejecta
and CSM, implying that they share similar circumstellar configurations. Our
preliminary estimate also suggests that the circumstellar environment of
SN2018evt has been significantly enriched at a rate of $\sim0.1$ M$_\odot$
yr$^{-1}$ over a period of $>100$ yr.
