orthicadj.
/ˈɔːθɪk/, U.S. /ˈɔrθɪk/ΘΚΠ
the world > the earth > minerals > mineral structure or appearance > [adjective] > cleavage or fracture > having cleavage at particular angles
paratomous1825
orthotomous1861
orthoclastic1866
orthic1877
1877 J. Le Conte Elements Geol. (1879) 204 (note) In this case syenite would differ from diorite only in the form of the feldspar, which in the former is orthic (orthoclase), and in the latter clinic (plagioclase).
2. Geometry.
a. Of a polyhedron: composed of pairs of equal parallel faces of which equivalent points are connected by lines perpendicular to the faces. Now rare.
ΚΠ
1894 Ld. Kelvin in Proc. Royal Soc. 55 13 The tetrakaidekahedron of which the twenty-four corners are the corners of the tetrahedrons thus placed may conveniently be called the orthic tetrahedron... It was described in..my paper on ‘The Division of Space with Minimum Partitional Area’, under the name of ‘plane-faced isotopic tetrakaidekahedron’; but I now prefer to call it orthic, because, for each of its seven pairs of parallel faces, lines forming corresponding points in the two faces are perpendicular to the faces, and the planes of its three pairs of square faces are perpendicular to one another.
1924 New Phytologist 23 157 Figures comparing models of orthic tetrakaidecahedra with models of the actual cells, show a close approximation to the tetrakaidecahedral form.
1942 J. Needham Biochem. & Morphogenesis iii. 536 The orthic hexoctahedron..is the ideal form taken up by compressed adjacent spheres of equal size so that the material aggregates with no waste spaces.
1986 Colloids & Surfaces 21 181 Available expressions [for volume and surface area] refer only to orthic polyhedra, that is, those with straight edges and plane faces, such as the orthic truncated octahedron.
b. Designating the triangle whose vertices are the feet of the altitudes of a given triangle.
ΘΚΠ
the world > relative properties > number > geometry > shape or figure > [adjective] > two-dimensional > triangular > other
nonelike1551
quadrantal1616
subcontrary1669
orthic1920
1920 Amer. Math. Monthly 27 199 The triangle DEF formed by the feet D, E, F, of the altitudes is frequently called the orthic triangle of ABC.
1956 Math. Mag. 29 289 If the orthic triangle is similar to the basic triangle, what is the value of the ratio of this similitude?
1998 J. L. Heilbron Geom. Civilized v. 218 A good example is a property of the so-called orthic triangle..made by connecting the feet of the altitudes of a triangles.
3. Soil Science. Of a soil: having the median characteristics of its type.
ΚΠ
1960 Soil Classif.: 7th Approximation (U.S. Dept. Agric.) 20/2 The soils lie outside the range of the Orthic subgroup and there is no class toward which they intergrade.
1970 Ecol. Monogr. 40 328/1 The Saussaurea moist meadow communities have young, poorly developed soils which most closely fit the description of an Orthic Ustochrept.
1993 New Scientist 11 Dec. 40/2 Predominantly sandy soils, such as the orthic podzols of Scandinavia, Finland, and northwestern Russia.
2003 Ground Water (Nexis) 41 72 Soils of the region are composed of orthic humo-ferric and ferro-humic podzols, gleyed humo-ferric podzols, and orthic gleysols.
This entry has been updated (OED Third Edition, September 2004; most recently modified version published online March 2022).
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adj.1877