*apotome*

‖n. [ Gr. 'apotomh` a cutting off, fr. 'apote`mnein to cut off; 'apo` from + te`mnein to cut. ] 1. (Math.) The difference between two quantities commensurable only in power, as between √2 and 1, or between the diagonal and side of a square. [ 1913 Webster ]

2. (Mus) The remaining part of a whole tone after a smaller semitone has been deducted from it; a major semitone. [ Obs. ] [ 1913 Webster ]