I don't know anything about being a BRD, but the rest of the BRD Threnodies have the same elemental attribute as the song itself. i.e. Earth Threnody is an earth-type song. So shouldn't Wind Threnody be a wind-type song?
Praetor is right there, wind threnody works by inflicting an ice aura on the mob, thus making that mob less resistant to wind attacks. Use this before Aero, silence or Earth threnody
Wha..? Don't you mean you cast this on a earth based mob and then use a wind based attack and there's less resistance? Why would you cast this then use an ice attack??