Source : Webster's Revised Unabridged Dictionary (1913)

   4. (Math.) A quantity greater than any assignable quantity of
      the same kind.

   Note: Mathematically considered, infinity is always a limit
         of a variable quantity, resulting from a particular
         supposition made upon the varying element which enters
         it. --Davies & Peck (Math. Dict.).

   5. (Geom.) That part of a line, or of a plane, or of space,
      which is infinitely distant. In modern geometry, parallel
      lines or planes are sometimes treated as lines or planes
      meeting at infinity.

   {Circle at infinity}, an imaginary circle at infinity,
      through which, in geometry of three dimensions, every
      sphere is imagined to pass.

   {Circular points at infinity}. See under {Circular}.

Circular \Cir"cu*lar\, a. [L. circularis, fr. circulus circle:
   cf. F. circulaire. See {Circle}.]
   1. In the form of, or bounded by, a circle; round.

   2. repeating itself; ending in itself; reverting to the point
      of beginning; hence, illogical; inconclusive; as, circular
      reasoning.

   3. Adhering to a fixed circle of legends; cyclic; hence,
      mean; inferior. See {Cyclic poets}, under {Cyclic}.

            Had Virgil been a circular poet, and closely adhered
            to history, how could the Romans have had Dido?
                                                  --Dennis.

   4. Addressed to a circle, or to a number of persons having a
      common interest; circulated, or intended for circulation;
      as, a circular letter.

            A proclamation of Henry III., . . . doubtless
            circular throughout England.          --Hallam.

   5. Perfect; complete. [Obs.]

            A man so absolute and circular In all those
            wished-for rarities that may take A virgin captive.
                                                  --Massinger.

   {Circular are}, any portion of the circumference of a circle.
      

   {Circular cubics} (Math.), curves of the third order which
      are imagined to pass through the two circular points at
      infinity.

   {Circular functions}. (Math.) See under {Function}.

   {Circular instruments}, mathematical instruments employed for
      measuring angles, in which the graduation extends round
      the whole circumference of a circle, or 360[deg].

   {Circular lines}, straight lines pertaining to the circle, as
      sines, tangents, secants, etc.

   {Circular} {note or letter}.
      (a) (Com.) See under {Credit}.
      (b) (Diplomacy) A letter addressed in identical terms to a
          number of persons.

   {Circular numbers} (Arith.), those whose powers terminate in
      the same digits as the roots themselves; as 5 and 6, whose
      squares are 25 and 36. --Bailey. --Barlow.

   {Circular points at infinity} (Geom.), two imaginary points
      at infinite distance through which every circle in the
      plane is, in the theory of curves, imagined to pass.

   {Circular polarization}. (Min.) See under {Polarization}.

   {Circular or Globular} {sailing} (Naut.), the method of
      sailing by the arc of a great circle.

   {Circular saw}. See under {Saw}.