1. Nine and ten united.

Nuttall's Standard dictionary of the English language By Nuttall, P.Austin

• ninetees,
• nighteen,
• ninetee,
• nineten,
• nineteeno,
• nicateen,
• ninteen,
• ninetheen,
• nicoteen,
• ninttenn,
• niteen,
• ninneteen,
• nineteeen,
• nemetaen,
• ninnther,
• Nineterrm,
• Kinetefon,
• ninetein,
• ninetenn,
• ninenteen

• nineteenth,
• ninety-one,
• ninety-nine.

The adjective form of the word "nineteen" is "nineteenth".

The plural form of the word "nineteen" is "nineteens"

The singular form of the word "nineteen" is "nineteen". The word does not change when referring to one item or quantity.