September is Etymology Month (11)

clan early 15c., from Gael. clann "family, stock, offspring," akin to O.Ir. cland "offspring, tribe," both from L. planta "offshoot". The Goidelic branch of Celtic (including Gaelic) had no initial p-, so it substituted k- or c- for Latin p-. The same Latin word in (non-Goidelic) Middle Welsh became plant "children."