Rule §18
Class X also includes many agent nouns formed by prefixing ka— to a verb root (e.g. kabila 'herdsman' from -bila 'to herd cattle'); this formation is common in the interior (sertão) but very rare in Loanda.
Chatelain’s original wording (1889)
Pertencem tambem a esta cl. muitos nomes derivados do radical do verbo, antepondo-lhe ka— e que significam o agente do que o verbo exprime. Ex.: kabila = pastor de gado, de-bila = pastar gado. Esta forma, commum no sertão, é rarissima em Loanda.