sinus

Etymology

Learned borrowing from Latin sinus (“a bent surface, curve, hollow”). Doublet of sine.

noun

1. (anatomy, zootomy) A pouch or cavity in a bone or other tissue, especially one in the bones of the face or skull connecting with the nasal cavities (the paranasal sinus).
2. (anatomy) An irregular venous or lymphatic cavity, reservoir, or dilated vessel.
   1. (physiology, attributive) Relating to or denoting the sinoatrial node of the heart or its function of regulating the heartbeat.
3. (pathology) An abnormal cavity or passage such as a fistula, leading from a deep-seated infection and discharging pus to the surface.
4. (botany) A rounded notch or depression between two lobes or teeth in the margin of a leaf or petal.
5. (geography) A bay of the sea; a recess in the shore.
6. (trigonometry) Synonym of sine.
   So, in the helicopteron, as the helix is at the same time a sustaining plane, it should be likened to a surface moving horizontally, and in which, consequenty, the resistance to motion will be to the lifting power as the sinus is to the cosinus of the angle formed by such plane with the horizon. 29 November 1884, “Aerial Navigation”, in Scientific American: A Weekly Journal of Practical Information, Art, Science, Mechanics, Chemistry, and Manufactures, volume LI, number 22, New York, N.Y.: Munn & Co., translation of original by Victor Tatin in La Nature, page 342, column 1
   The variations are described in terms of cycles of sinuses and cosinuses. 1996, Pentti Zetterberg, Matti Eronen, Markus Lindholm, “Construction of a 7500-Year Tree-Ring Record for Scots Pine (Pinus sylvestris, L.) in Northern Fennoscandia and its Application to Growth Variation and Palaeoclimatic Studies”, in Heinrich Spiecker, Kari Mielikäinen, Michael Köhl, Jens Peter Skovsgaard, editors, Growth Trends in European Forests (European Forest Institute Research Report; No. 5), Springer-Verlag Berlin Heidelberg, page 15
   Basically, the rotation of the matrix of the factor loadings L represents its post-multiplication, i.e. L* = LO by the rotation matrix O, which itself resembles one of the matrices included in the classical rotational Lie groups SO(m) (containing the specific m–fold combination of sinuses and cosinuses. 2007, Vladimir G. Ivancevic, Tijana T. Ivancevic, “Introduction: Human and Computational Mind”, in Computational Mind: A Complex Dynamics Perspective (Studies in Computational Intelligence; 60), Springer-Verlag Berlin Heidelberg, →LCCN, section 1 (Natural Intelligence and Human Mind), pages 60–61