资料来源 : Webster's Revised Unabridged Dictionary (1913)

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 =
       ax^{n} where n is a positive whole number or a positive
       fraction. For the {cubical parabola} n = 3; for the
       {semicubical parabola} n = 3/2. See under {Cubical}, and
       {Semicubical}. The parabolas have infinite branches, but
       no rectilineal asymptotes.