The etymological dictionary of Corominas says the origin is uncertain, but it suggests that it comes from the Vulgar Latin cappula, plural of cappulum, "sword hilt".
O dicionario etimolóxico de Corominas afirma que se trata dunha palabra de orixe incerta, e suxire que vén do latín vulgar cappula, plural de cappulum, empuñadura de espada.