  Spin-orbit coupling (SOC) offers a large variety of novel and extraordinary
magnetic and electronic properties in otherwise `ordinary pool' of heavy ion
oxides. Here we present a detailed study on an apparently isolated hexagonal
2$H$ spin-chain $d^4$ iridate Sr$_3$LiIrO$_6$ (SLIO) with geometric
frustration. Our structural studies clearly reveal perfect Li-Ir chemical order
in this compound. Our combined experimental and {\it ab-initio} electronic
structure investigations establish a magnetic ground state with finite
Ir$^{5+}$ magnetic moments in this compound, contrary to the anticipated
nonmagnetic $J$=0 state. Furthermore, the dc magnetic susceptibility ($\chi$),
heat capacity ($C_p$) and spin-polarized density functional theory (DFT)
studies unravel that despite having noticeable antiferromagnetic correlation
among the Ir$^{5+}$ local moments, this SLIO system evades any kind of magnetic
ordering down to at least 2 K due to geometrical frustration, arising from the
comparable interchain Ir-O-O-Ir superexchange interaction strengths, hence
promoting SLIO as a potential quantum spin liquid candidate.
