Friedrich Kluge, An Etymological Dictionary of the German Language (1891)
“ It is true that in MidHG. káppelle (ModAlem. käppelle) , with the G. accent also occurs, and hence the UpG. Kappel, Käppel, frequent names of villages. MidLat. capella has a peculiar history; as a dimin. of capa (comp. Kappe) it signified ‘a cape’; the chapel itself, in which the cloak of St. Martin and other relics were preserved, first obtained the name of capella; then from about the 7th cent. ”
