'Capital' comes from the Latin word caput, meaning head. The head is crucial to life, and 'capital', accumulated wealth, is crucial to a business. In this sense, 'capital' started as a piece of 16th-century business jargon.
It came from the Venetian system of accounting, the hot management tool of the day. 'Capital' subsequently came to stand for any source of power - 'political capital', 'social capital', 'human capital' - as well as, with a big C, for wealth creators as a class, doomed to struggle for ever with Labour, with a big L.
Those were the days. Or not.