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The curve which a body describes in space, as a planet or comet in its orbit, or stone thrown upward obliquely in the air.

A plane figure bounded by four right lines, of which no two are parallel.

A tetartohedral solid of the hexagonal system, bounded by six trapezoidal planes. The faces of this form are common on quartz crystals.

A plane four-sided figure, having two sides parallel to each other.

To plane in a direction across the grain of the wood; as, to traverse a board.

Trine, an aspect of two planets distant 120 degrees from each other. Hutton.

n. -- Trigonometrical lines, lines which are employed in solving the different cases of plane and spherical trigonometry, as sines, tangents, secants, and the like. These lines, or the lengths of them, are trigonometrical functions of the arcs and angles to which they belong. -- Trigonometrical survey. See under Surv…

metry which treats of the relations and properties of the trigonometrical functions. -- Plane trigonometry, and Spherical trigonometry, those branches of trigonometry in which its principles are applied to plane triangles and spherical triangles respectively.

Having three sides or faces; thus, a trihedral angle is a solid angle bounded by three plane angles. [Written also triedral.]

The aspect of planets distant from each other 120 degrees, or one third of the zodiac; trigon. In sextile, square, and trine. Milton.

An aspect of two planets with regard to the earth when they are three octants, or three eighths of a circle, that is, 135 degrees, distant from each other. Hutton.

Three sided, the sides being plane or concave; having three salient angles or edges; trigonal.

moving curve rolls without slipping on a second fixed curve, the curves all being in one plane. Cycloids, epicycloids, hypocycloids, cardioids, etc., are all trochoids.

Replaced, or cut off, by a plane, especially when equally inclined to the adjoining faces; as, a truncated edge.

The replacement of an edge or solid angle by a plane, especially when the plane is equally inclined to the adjoining faces.

-- Twin-screw steamer, a steam vessel propelled by two screws, one on either side of the plane of the keel.

g, twinning of more than two crystals, or parts of crystals. -- Twinning axis, Twinning plane. See the Note under Twin, n.

ed to torsion; hence, perverted. Twisted curve (Geom.), a curve of double curvature. See Plane curve, under Curve. -- Twisted surface (Geom.), a surface described by a straight line moving according to any law whatever, yet so that the consecutive positions of the line shall not be in one plane; a warped surface.…

part of the heavens that is more than eight degrees from the ecliptic; as, ultrazodiacal planets, that is, those planets which in part of their orbits go beyond the zodiac.

The conical shadow projected from a planet or satellite, on the side opposite to the sun, within which a spectator could see no portion of the sun's disk; -- used in contradistinction from penumbra. See Penumbra.