Source : Webster's Revised Unabridged Dictionary (1913)

Spiral \Spi"ral\, n. [Cf. F. spirale. See {Spiral}, a.]
   1. (Geom.) A plane curve, not re["e]ntrant, described by a
      point, called the generatrix, moving along a straight line
      according to a mathematical law, while the line is
      revolving about a fixed point called the pole. Cf.
      {Helix}.

   2. Anything which has a spiral form, as a spiral shell.

   {Equiangular spiral},a plane curve which cuts all its
      generatrices at the same angle. Same as {Logarithmic
      spiral}, under {Logarithmic}.

   {Spiral of Archimedes}, a spiral the law of which is that the
      generatrix moves uniformly along the revolving line, which
      also moves uniformly.

Equiangular \E`qui*an"gu*lar\, a. [Equi- + angular. Cf.
   {Equangular}.]
   Having equal angles; as, an equiangular figure; a square is
   equiangular.

   {Equiangular spiral}. (Math.) See under {Spiral}, n.

   {Mutually equiangular}, applied to two figures, when every
      angle of the one has its equal among the angles of the
      other.