Apotome /(ȧ*pŏt"ō̇*mē̇)/

A·pot·o·me

Apotome

n.
  1. The difference between two quantities commensurable only in power, as between √2 and 1, or between the diagonal and side of a square. (Math.)
  2. The remaining part of a whole tone after a smaller semitone has been deducted from it; a major semitone. (Mus) [Obs.]