apotome

Noun

apotome (plural apotomes)

1. The difference between two quantities or lengths commensurable only in power, as between 1 and the square root of 2, or between the diagonal and side of a square.
   • Yet it is not until Book X that the properties of such a line (with greater length is an apotome and lesser length a first apotome) are explained and not until Book XIII that this type of line is applied, which will be discussed in more detail later.[…]The likewise is true of apotomes (X. 97).2012, Jade Roskam, “Book X of The Elements: Ordering Irrationals”, in Bharath Sriraman, editor, Crossroads in the History of Mathematics and Mathematics Education, Information Age Publishing, page 210
   • If some number and the root of the root of a number are multiplied by the corresponding apotome, the result will be an apotome.2014, Jacques Sesiano (translator), Liber Mahameleth, Part Two: Translation, Glossary, [12th c, Anonymous (possibly John of Seville), Liber Mahameleth], Springer, page 767
2. The remaining part of a whole tone after a minor second has been deducted from it; an augmented unison. Most commonly used to refer to the Pythagorean chromatic semitone, which has a ratio of 2187/2048.
   • This semitone was termed by the Pythagoreans apotome, and the diatonic semitone was termed limma. They contended, that the apotome, or distance from B flat to B natural, was larger than the limma, or distance from A to B flat.1813, Music, article in John Mason Good, Olinthus Gregory, Newton Bosworth, Pantologia: A New Cyclopaedia, Volume 8: MID—OZO, unnumbered page
   • For the ratio of the excess of the apotome, above that which is truly a semitone, and which cannot be obtained in numbers, is thus called. This then is demonstrated. To what has been said however, it must be added, that we have called the ratio of d b a semitone, not that a sesquioctave is divided...1820, Proclus, translated by Thomas Taylor, The Commentaries of Proclus on the Timæus of Plato, Volume 2, Facsimile edition, published 1967, pages 66–67
3. A distinct division of an insect which is divided from the other divisions by a pinch point.
   • The bands pass inside the margins of the apotome as they approach its constriction and form two pigmented areas broadly based on the frontal sutures and becoming dispersed towards the mid-line.1964, Proceedings of the Zoological Society of London, Zoological Society of London, page 287
   • In generalized Diplura, Archaeognatha and some Thysanura, five parts or apotomes are distinguished, which from the anterior to the posterior part are: the presternum, the basisternum, the furcasternum, the spinasternum and the poststernum.2008, John L. Capinera, Encyclopedia of Entomology, →ISBN, page 3766