of director, from directus, direct. Dodecahedron (dō'dek-a-he'dron). G. dodeka, twelve, + hedra, a seat.

Equal (e'kwal). L. æqualis, equal,

from æquus, plain. Equiangular (e-kwi-ang'gu-lär). L. æquus, equal, + angulus, angle. Equilateral (e-kwi-lat ́e-ral). L. æquus, equal, + latus, side. Equivalent

(e-kwiv'a-lent). L. æquus, equal, +valere, be strong. Escribed (es-kribd'). L. e, out, + scribere, write.

Excess (ek-ses'). L. ex, out, + cedere, go; i.e. to pass beyond. Frustum (frus'tum). L. a piece. Generatrix (jen'e-ra-triks). L. fem. of generator, from generare, beget, from genus, a race. Geometry (je-om'e-tri). G. ge, the

earth, metron, a measure. -gon, a termination, G. gonia, an angle.

Harmonic (här-mon'ik). G. har

monia, a concord, related to har

:

mos, a joining. A line divided internally and externally in the ratio 2 1, is cut into segments representing 1, †, . Pythagoras first discovered that a vibrating string stopped at half its length gave the octave of the original note, and stopped at two-thirds of its length gave the fifth. Hence the expression "harmonic division" of a line. Hemisphere (hem'i-sfēr). G. hemi-, half, + sphaira, a sphere. -hedron, a termination, G. hedra, a seat.

Hepta-, in combination, G. seven. Hexa-, in combination, G. six. Hexagram (hek'sa-gram). G. hex, six, +gramma, a line. Homology (hō-mol'ō-ji), G. homos, the same, legein, speak. Hypotenuse (hi-pot'e-nūs). G. hypo, under, teinein, stretch. Inclination (in-kli-na'shọn). L. in, on, clinare, lean. Incommensurable (in-kō-men ́sura-bl). L. in-, not, + com-, together, mensurare, measure. Infinity (in-fin'i-ti). L. in-, not, +finitus, bounded.

Minimum (min'i-mum). L. least.
Minor (minor). L. less.
Nappe (nap). French, a cloth,
sheet, surface.

Oblique (ob-lek' or ob-lik'). L. ob,

before, +liquis, slanting. Obtuse (ob-tus'). L. obtusus, blunt, from ob, upon, + tundere, strike. Octo-, octa-, in combination, L. and G., eight.

Opposite (op'o-zit). L. ob, before, against, ponere, put, set. Ordinate (ôr'di-nat).

din-), a row.

L. ordo (or

G.

Orthocenter (ôr'thō-sen-ter).

ortho-, straight, + kentron, center. Orthogonal (ôr-thog'ō-nal). G. orthos, right, + gonia, an angle. Parallel (para-lel). G. para, beside,+ allelon, one another. Parallelepiped (par-a-lel-e-pip'ed or -pi'ped). Gr. parallelos, parallel, + epipedon, a plane surface, from epi, on, + pedon, ground. Parallelogram

(par-a-lel'o-gram).

G. parallelos, parallel, +gramma, line.

Pedal (ped'al or pedal). L. pedalis, pertaining to the foot, from pes (ped-), foot. Pencil (pen'sil). L. penicillum, a painters' pencil, a brush.

Perigon (per'i-gon). G. peri, around, +gonia, a corner, angle. Perimeter (pe-rim'e-tér). G. peri, around, + metron, measure. Perpendicular (per-pen-dik'u-lär). L. perpendiculum, a plumb-line, from per, through, + pendere, hang. Perspective (per-spektiv). L. per, through, specere, see. π (pi). Initial of G. periphereia, periphery, circumference.

Pole (pōl). G. polos, a pivot, hinge, axis, pole.

Polygon (pol'i-gon). G. polys,

many, gonia, corner, angle. Polyhedron (pol-i-he'dron). G. polys, many, hedra, seat. Postulate (pos'tu-lat). L. postulatum, a demand, from poscere, ask. Prism (prizm). G. prisma, something sawed, from priein, saw. Prismatoid (priz'ma-toid). G. prisma (t-), + eidos, form. Projection (pro-jek'shon). L. pro, forth, jacere, throw. Pyramid (pir'a-mid). G. pyramis, a pyramid, perhaps from Egyptian pir-em-us, the slanting edge of a pyramid.

Quadrant (kwod'rant). L. quadran(t-)s, a fourth part. See Quadrilateral.

Quadrilateral (kwod-ri-lat'e-ral). L. quattuor (quadri-), four, + latus (later-), side. Radius (ra'di-us). L. rod, spoke of a wheel.

Ratio (rā'shiō). L. a reckoning, calculation, from reri, think, estimate.

Reciprocal (re-sip'ro-kal). L. reciprocus, returning, from re-, back, and pro, forward, with two adjective terminations. Rectangle (rek'tang-gl). L. rectus, right, angulus, an angle. See Angle. Rectilinear (rek-ti-lin'e-är). L. rectus, right, linea, a line.

Reflex (re'fleks or re-fleks'). L. re-, back, +flectere, bend. Regular (reg'u-lär). L. regula, a rule, from regere, rule, govern. Rhombus (rom'bus). G. rhombos,

a spinning top.

Scalene (ska-lēn ́). G. skalenos, uneven, unequal; related to skellos, crooked-legged.

Secant (se kant). L. secare, cut,

as also Sector, Section, Segment. Segment (segment). See Secant. Semicircle (sem'i-ser-kl). L. semi-, half, circulus, circle.

Similar (sim'i-lär). L. similis, like. Solid (solid). L. solidus, firm, compact.

Sphere (sfer). G. sphaira, a ball. Square (skwar). L. quadra, a square, from quattuor, four. Straight (strāt). Anglo-Saxon, streht, from streccan, stretch. Subtend (sub-tend'). L. sub, under, + tendere, stretch.

Successive (suk-ses'iv). L. sub, under, cedere, go. Sum (sum). L. summa, highest part. Compare Summit.

G.

Tetrahedron (tet-ra-hē'dron). tetra-, four, + hedra, seat. Theorem (the ō-rem). G. theorema, a sight, a principle contemplated. Transversal

(trans-vér'sal). L.

trans, across, + vertere, turn. Trapezium (tra-pē'zi-um). G. trapezion, a table, dim. of trapeza, a table, from tetra, four, + pous, foot.

Trapezoid (tra-pē ́zoid). G. trapeza,

table,+ eidos, form.

Tri-, in composition, L. tres (tri-), G. treis (tri-), three. See Secant, -hedron, Angle, for meaning of trisect, etc.

Truncate (trung'kāt). L. truncare, cut off, from Old L. troncus, cut mutilated.

off,

Unique (u-nēk'). L. unicus, from unus, one.

Vertex (ver'teks). L. vertere, turn. Zone (zōn). G. zone, a girdle,

belt.