  We present long-term photometric and spectroscopic studies of Circumstellar
Material (CSM)-Ejecta interacting supernova (SN) ASASSN-14il in the galaxy PGC
3093694. The SN reaches a peak $r$-band magnitude of $\sim$ $-20.3 \pm 0.2$ mag
rivaling SN 2006tf and SN 2010jl. The multiband and the pseudo-bolometric
lightcurve show a plateau lasting $\sim 50$ days. Semi-analytical CSM
interaction models can match the high luminosity and decline rates of the
lightcurves but fail to faithfully represent the plateau region and the bumps
in the lightcurves. The spectral evolution resembles the typical SNe IIn
dominated by CSM interaction, showing blue-continuum and narrow Balmer lines.
The lines are dominated by electron scattering at early epochs. The signatures
of the underlying ejecta are visible as the broad component in the H$\alpha$
profile from as early as day 50, hinting at asymmetry in the CSM. A narrow
component is persistent throughout the evolution. The SN shows remarkable
photometric and spectroscopic similarity with SN 2015da. However, the different
polarization in ASASSN-14il compared to SN 2015da suggests an alternative
viewing angle. The late-time blueshift in the H$\alpha$ profiles supports dust
formation in the post-shock CSM or ejecta. The mass-loss rate of 2-7 M$_{\odot}
\mathrm{yr}^{-1}$ suggests a Luminous Blue Variable (LBV) progenitor in an
eruptive phase for ASASSN-14il.
