# Parabola

## Pa*rab"o*la

(?), n.;
pl. Parabolas (#).
[NL., fr. Gr. ; -- so called because its axis is parallel to the side of the cone. See Parable, and cf. Parabole.] (Geom.) (a) A kind of curve; one of the conic sections formed by the intersection of the surface of a cone with a plane parallel to one of its sides. It is a curve, any point of which is equally distant from a fixed point, called the focus, and a fixed straight line, called the directrix. See Focus. (b) One of a group of curves defined by the equation y = axn where n is a positive whole number or a positive fraction. For the cubical parabola n = 3; for the semicubical parabola n = . See under Cubical, and Semicubical. The parabolas have infinite branches, but no rectilineal asymptotes.
[1913 Webster]

## Pa*rab"o*le

(?), n. [L., fr. Gr. . See Parable.] (Rhet.) Similitude; comparison.
[1913 Webster]

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## Par`a*bol"ic*al

(?), } a. [Gr. paraboliko`s figurative: cf. F. parabolique. See Parable.]
[1913 Webster]

1. Of the nature of a parable; expressed by a parable or figure; allegorical; as, parabolical instruction.
[1913 Webster]

2. [From Parabola.] (Geom.) (a) Having the form or nature of a parabola; pertaining to, or resembling, a parabola; as, a parabolic curve. (b) Having a form like that generated by the revolution of a parabola, or by a line that moves on a parabola as a directing curve; as, a parabolic conoid; a parabolic reflector; a parabolic antenna.
[1913 Webster +PJC]

Parabolic conoid, a paraboloid; a conoid whose directing curve is a parabola. See Conoid. -- Parabolic mirror (Opt.), a mirror having a paraboloidal surface which gives for parallel rays (as those from very distant objects) images free from aberration. It is used in reflecting telescopes. -- Parabolic spindle, the solid generated by revolving the portion of a parabola cut off by a line drawn at right angles to the axis of the curve, about that line as an axis. -- Parabolic spiral, a spiral curve conceived to be formed by the periphery of a semiparabola when its axis is wrapped about a circle; also, any other spiral curve having an analogy to the parabola.
[1913 Webster]

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Sun 12th July 2020