1. [n]  position 19 in a countable series of things
2. [adj]  coming next after the eighteenth in position

NINETEENTH is a 10 letter word that starts with N.

1. \Nine"teenth`\, a. [Cf. AS. nigonte['o]?a.]
   1. Following the eighteenth and preceding the twentieth;
      coming after eighteen others.
   
   2. Constituting or being one of nineteen equal parts into
      which anything is divided.
   
   

2. \Nine"teenth`\, n.
   1. The quotient of a unit divided by nineteen; one of
      nineteen equal parts of anything.
   
   2. The next in order after the eighteenth.
   
   3. (Mus.) An interval of two octaves and a fifth.