1. (a.) Next in order after the twelfth; the third after the tenth; -- the ordinal of thirteen; as, the thirteenth day of the month.

2. (a.) Constituting or being one of thirteen equal parts into which anything is divided.

3. (n.) The quotient of a unit divided by thirteen; one of thirteen equal parts into which anything is divided.

4. (n.) The next in order after the twelfth.

5. (n.) The interval comprising an octave and a sixth.