What does "thirteenth" mean?

Thirteenth: Constituting or being one of thirteen equal parts into which anything is divided.

Additional senses

  1. 2.The quotient of a unit divided by thirteen; one of thirteen equal parts into which anything is divided.
  2. 3.The next in order after the twelfth.
  3. 4.(Mus.) The interval comprising an octave and a sixth.

Sources