planxty (n.)

in Irish music, "harp tune of a sportive and animated character" [OED], 1790, of unknown origin, evidently not a native Irish word. According to OED, some suggest ultimate derivation from Latin plangere "to strike, beat" (from PIE root *plak- (2) "to strike"). See also Katrin Thier, "Of Picts and Penguins -- Celtic Languages in the New Edition of the OED," in "The Celtic Languages in Contact," 2007.