"twenty-sided body," 1560s, from Latinized form of Greek eikosahedron, noun use of neuter of eikosahedros, from eikosi "twenty" + -hedra "seat, base, chair, face of a geometric solid," from PIE root *sed- (1) "to sit." Greek eikosi is from PIE *wikmti- "twenty," from *wi- "in half" (hence "two") + (d)kmti-, from root *dekm- "ten" (from PIE root *dekm- "ten"). Related: icosahedral.
"triangular pyramid, solid figure contained by four triangular surfaces," 1560s, from Late Greek tetraedron, noun use of neuter of tetraedros (adj.) "four-sided," from tetra- "four" (from PIE root *kwetwer- "four") + hedra "seat, base, chair, face of a geometric solid," from PIE root *sed- (1) "to sit." Related: Tetrahedral.
"a solid bounded by many (usually more than 6) plane faces," 1560s, from Latinized form of Greek polyedron, neuter of adjective polyedros "having many bases or sides," from polys "many" (from PIE root *pele- (1) "to fill") + hedra "seat, base, chair, face of a geometric solid" (from PIE root *sed- (1) "to sit").
geometric figure, "oblique-angled equilateral parallelogram," 1570s, from French rhombe, from Latin rhombus "a magician's circle," also a kind of fish, which in Late Latin took on also the geometric sense. This is from Greek rhombos "circular movement, spinning motion; spinning-top; magic wheel used by sorcerers; tambourine;" also "a geometrical rhomb," also the name of a flatfish.
Watkins has this from rhembesthai "to spin, whirl," from PIE *wrembh-, from *werbh- "to turn, twist, bend" (source also of Old English weorpan "to throw away"), from root *wer- (2) "to turn, bend" (see versus). But Beekes connects rhombos to rhembomai "to go about, wander, roam about, act random," despite this being attested "much later," a word of no clear etymology.
In general use in reference to any lozenge-shaped object. Related: Rhombic.
genus of low, branchy desert shrubs, 1914, from Modern Latin (1737) from Greek ephedra, a name given by Pliny to the horsetail, literally "sitting upon," from fem. of ephedros "sitting or seated upon; sitting at or near," from epi "on" (see epi-) + hedra "seat, base, chair; face of a geometric solid," from PIE root *sed- (1) "to sit." The reason for the name is not known.
"early 20c. revolutionary movement in visual arts characterized (at first) by simple geometric forms," 1911, from French cubisme, from cube (see cube (n.) + -ism). Said to have been coined by French art critic Louis Vauxcelles at the 1908 Salon des Indépendants in reference to a work by Georges Braque. Related: Cubist (by 1914 as an adjective, 1920 as a noun).
Chinese geometric puzzle, 1864, said to be an arbitrary formation based on anagram, etc. First element perhaps Chinese t'an "to extend," or t'ang, commonly used in Cantonese for "Chinese." Some suggest it is the name of the inventor, "but no such person is known to Chinese scholars" [OED]. Another theory involves the Tanka, an outcast aboriginal people of southern China, and Western sailors who discovered the puzzle from their Tanka girlfriends. Perhaps from an obscure sense of tram. The Chinese name is Ch'i ch'iao t'u "seven ingenious plan."
1610s, "an illustrative figure giving only the outlines or general scheme of the object;" 1640s in geometry, "a drawing for the purpose of demonstrating the properties of a figure;" from French diagramme, from Latin diagramma "a scale, a musical scale," from Greek diagramma "geometric figure, that which is marked out by lines," from diagraphein "mark out by lines, delineate," from dia "across, through" (see dia-) + graphein "write, mark, draw" (see -graphy). Related: Diagrammatic; diagrammatically.
The verb, "to draw or put in the form of a diagram," is by 1822, from the noun. Related: Diagrammed; diagramming.
1590s, "cross-shaft, straight rod or bar," from Latin radius "staff, stake, rod; spoke of a wheel; ray of light, beam of light; radius of a circle," a word of unknown origin. Perhaps related to radix "root," but de Vaan finds that "unlikely." The classical plural is radii.
The geometric sense of "straight line drawn from the center of a circle to the circumference" is recorded from 1650s. Meaning "circular area of defined distance around some place" is attested from 1853. As the name of the shorter of the two bones of the forearm from 1610s in English (the Latin word had been used thus by the Romans).