D defs.my
Entry 2 senses Webster, 1913

Apotome

/(ȧ*pŏt"ō̇*mē̇)/ · A·pot·o·me · IPA /əˈpɒtəmi/
01 n. The difference between two quantities commensurable only in power, as between √2 and 1, or between the diagonal and side of a square.
  1. 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. 2.
    The remaining part of a whole tone after a smaller semitone has been deducted from it; a major semitone.(Mus) [Obs.]