ἀποτομή, in Geometry, the difference between two incommensurable lines.

a term used by the ancient Greek theoretical writers on musical sounds and intervals to signify that interval in the ratio of 2187 : 2048, which, being cut off from the major tone 9 : 8, left the interval called a limma, λίμμα, or minor semitone, in the ratio 256 : 243. Also, the interval 125 : 128 was called a major apotome, and 2025 : 2048 a minor apotome.

APOTROPÆ (from ἀποτρέπω, I avert), in Ancient Poetry, verses composed for averting the wrath of incensed deities; and the deities invoked for averting any threatened misfortune were called Apotropæi. They were also called Alexicaci, from ἀλέγω, I drive away; and Averuncii, from averuncio, which denotes the same.