In his 1970 article Golden Rosaries of the Bka' brgyud schools, E. Gene Smith discusses the two forms of the name, and : A note is in order regarding the two forms Dkar brgyud pa and Bka' brgyud pa.
One source indicates: [T]he term "Kagyu" derives from the Tibetan phrase meaning "Lineage of the Four Commissioners" (Ka-bab-shi-gyu-pa).