- next after the twelfth; being the ordinal number for 13.
- being one of 13 equal parts.
- a thirteenth part, especially of one (1/13).
- the thirteenth member of a series.
- (usually prenominal)
- coming after the twelfth in numbering or counting order, position, time, etc; being the ordinal number of thirteen: often written 13th
- (as noun)
- one of 13 equal or nearly equal parts of something
- (as modifier)
- the fraction equal to one divided by 13 (1/13)
- music
- an interval of one octave plus a sixth
- short for thirteenth chord
