Grueslayer was the legendary blade of Entharion the Wise.
With this sword he single-handedly slew many ravenous grues.
Although the blade itself is long lost, its Sheath survived at least until 966 GUE, when it was seen on sale in an Accardi weapons shop. If the blade Grueslayer were to resurface, it would definitely worth at least half the wealth of the kingdom of Quendor.
The Sheath, as probably with the Blade as well, had magical powers: he who wears it is blessed with wondrous powers of recuperation.