  The first study of thermal conductivity, $\kappa$, in a quasi-two-dimensional
organic superconductor of the $\kappa$-(BEDT-TTF)$_2$X family reveals features
analogous to those already observed in the cuprates. The onset of
superconductivity is associated with a sudden increase in $\kappa$ which can be
suppressed by the application of a moderate magnetic field. At low
temperatures, a finite linear term - due to a residual electronic contribution-
was resolved. The magnitude of this term is close to what is predicted by the
theory of transport in unconventional superconductors.
