Entry record from Schapper (2020): Wersing Peitoko
-kaku[-ˈkaku]
• n. younger sibling (male or female).adik (lakilaki atau perempuan).
ekakuyour younger sibling, adik engkau
nekaku lmimy younger brother, adik laki-laki saya
nekaku meimy younger sister, adik perempuan saya
See also: -nang
Source: Hans Retebana