  Using the phonon Boltzmann transport formalism and density functional theory
based calculations, we show that stanene has a low thermal conductivity. For a
sample size of 1$\times$1 $\mu$m$^{2}$ ($L\times W$), the lattice thermal
conductivities along the zigzag and armchair directions are 10.83 W/m-K and 9.2
W/m-K respectively, at room temperature, indicating anisotropy in the thermal
transport. The low values of thermal conductivity are due to large
anharmonicity in the crystal resulting in high Gr\"{u}neisen parameters, and
low group velocities. The room temperature effective phonon mean free path is
found to be around 17 nm indicating that the thermal transport in stanene is
completely diffusive in nature. Furthermore, our study brings out the relative
importance of the contributing phonon branches and reveals that, at very low
temperatures, the contribution to lattice thermal conductivity comes from the
flexural acoustic (ZA) branch and at higher temperatures it is dominated by the
longitudinal acoustic (LA) branch. We also show that lattice thermal
conductivity of stanene can further be reduced by tuning the sample size and
creating rough surfaces at the edges. Such tunability in the lattice thermal
conductivity in stanene suggests its applications in thermoelectric devices.
