nineteenth (adj., n.)

"next in order or rank after the eighteenth; the ordinal numeral corresponding to nineteen; being one of nineteen equal parts into which a whole is regarded as divided;" late 14c., nyntenthe; from nineteen + -th (1).

It is a replacement or modification (by influence of nineteen) of nigonteoþa, nyenteoþe (c. 1300), from Old English nigon-teoða, which is cognate with Old Frisian niuguntinda, Dutch negentiende, Old High German niuntazehanto, German neunzehnte, Old Norse nitjandi, Danish nittende. Nineteenth hole "bar-room in a golf clubhouse" is attested from 1901.