'nineteenth' originates from Old English, specifically the word 'nigon-teoþa,' where 'nigon' meant 'nine' and 'teoþa' meant 'tenth.'

'nigon-teoþa' transformed into the Middle English word 'nigontenthe,' and eventually became the modern English word 'nineteenth.'

Initially, it meant 'the tenth after nine,' and this meaning has largely remained the same in modern usage.