brat: [16] The origins of brat are not altogether clear, but it has plausibly been connected with the English dialect brat ‘makeshift or ragged garment’, as being the sort of apparel a rough or ill-mannered child might wear. This brat first appeared in late Old English as bratt, meaning ‘cloak’, a borrowing from Old Irish bratt ‘covering, mantle’. [brat etymology, brat origin, 英语词源]