noun an interval consisting of two octaves.
2. fifteenth ·noun a stop in an organ tuned two octaves above the diaposon.
3. fifteenth ·adj next in order after the fourteenth;
the ordinal of fifteen.
4. fifteenth ·adj consisting of one of fifteen equal parts or divisions of a thing.
5. fifteenth ·noun one of fifteen equal parts or divisions; the quotient of a unit divided by fifteen.
6. fifteenth ·noun a species of tax upon personal property formerly laid on towns, boroughs, ·etc., in england, being one fifteenth part of what the personal property in each town, ·etc., had been valued at.