Adventurer's Dirge is a Bard song in Final Fantasy XI. It is available only to bards who have reached level 75 and who have gained additional merit points and designated they want to learn this ability. It is a tier two skill. As such, it may be initially purchased for 3 points, and then upgraded twice for 4 and then 5 points.
Adventurer's Dirge, in a way, is the cardinal opposite of the other 75 Bard merit song, Foe Sirvente. Adventurer's Dirge is a single target song. The effected player character will lose enmity at an increased rate than normal. In other words, this song is used to help the shed hate from one character who does not want the mobs attention or help said character to avoid gaining hate in the first place.