A singing sword was a magic +1 greatsword made of silver. It sang constantly (and loudly) when it was drawn, and gave its wielder a morale bonus, and a larger morale bonus against spells or effects affecting the mind. It was worth around 25,000 gold pieces.
The goddess Eilistraee gifted twenty holy singing bastard swords to Qilue Veladorn and the drow of the Promenade of the Dark Maiden. The blades' song made its wielder confident and immune to charm, command, confusion, fear, friends, repulsion, scare and suggestion. An emotion cast on the wielder only caused rage, focused on the one who cast the emotion spell. The sword's song also cancelled the effects of a harpy's song, silenced shriekers, and could entrance weak, earthly, living creatures, although this ability could be negated by a bard's counter-song.