The Collaborative International Dictionary of English v.0.48:

Polar \Po"lar\, a. [Cf. F. polaire. See Pole of the earth.]
   1. Of or pertaining to one of the poles of the earth, or of a
      sphere; situated near, or proceeding from, one of the
      poles; as, polar regions; polar seas; polar winds.
      [1913 Webster]

   2. Of or pertaining to the magnetic pole, or to the point to
      which the magnetic needle is directed.
      [1913 Webster]

   3. (Geom.) Pertaining to, reckoned from, or having a common
      radiating point; as, polar coordinates.
      [1913 Webster]

   Polar axis, that axis of an astronomical instrument, as an
      equatorial, which is parallel to the earths axis.

   Polar bear (Zool.), a large bear (Ursus maritimus syn.
      Thalarctos maritimus) inhabiting the arctic regions. It
      sometimes measures nearly nine feet in length and weighs
      1,600 pounds. It is partially amphibious, very powerful,
      and the most carnivorous of all the bears. The fur is
      white, tinged with yellow. Called also White bear. See
      Bear.

   Polar body, Polar cell, or Polar globule (Biol.), a
      minute cell which separates by karyokinesis from the ovum
      during its maturation. In the maturation of ordinary ova
      two polar bodies are formed, but in parthogenetic ova only
      one. The first polar body formed is usually larger than
      the second one, and often divides into two after its
      separation from the ovum. Each of the polar bodies removes
      maternal chromatin from the ovum to make room for the
      chromatin of the fertilizing spermatozoon; but their
      functions are not fully understood.

   Polar circles (Astron. & Geog.), two circles, each at a
      distance from a pole of the earth equal to the obliquity
      of the ecliptic, or about 23[deg] 28', the northern called
      the arctic circle, and the southern the antarctic circle.


   Polar clock, a tube, containing a polarizing apparatus,
      turning on an axis parallel to that of the earth, and
      indicating the hour of the day on an hour circle, by being
      turned toward the plane of maximum polarization of the
      light of the sky, which is always 90[deg] from the sun.

   Polar coordinates. See under 3d Coordinate.

   Polar dial, a dial whose plane is parallel to a great
      circle passing through the poles of the earth. --Math.
      Dict.

   Polar distance, the angular distance of any point on a
      sphere from one of its poles, particularly of a heavenly
      body from the north pole of the heavens.

   Polar equation of a line or Polar equation of a surface,
      an equation which expresses the relation between the polar
      coordinates of every point of the line or surface.

   Polar forces (Physics), forces that are developed and act
      in pairs, with opposite tendencies or properties in the
      two elements, as magnetism, electricity, etc.

   Polar hare (Zool.), a large hare of Arctic America (Lepus
      arcticus), which turns pure white in winter. It is
      probably a variety of the common European hare (Lepus
      timidus).

   Polar lights, the aurora borealis or australis.

   Polar opposition, or Polaric opposition or Polar
   contrast or Polaric contrast (Logic), an opposition or
      contrast made by the existence of two opposite conceptions
      which are the extremes in a species, as white and black in
      colors; hence, as great an opposition or contrast as
      possible.

   Polar projection. See under Projection.

   Polar spherical triangle (Spherics), a spherical triangle
      whose three angular points are poles of the sides of a
      given triangle. See 4th Pole, 2.

   Polar whale (Zool.), the right whale, or bowhead. See
      Whale.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Polar \Po"lar\, n. (Conic Sections)
   The right line drawn through the two points of contact of the
   two tangents drawn from a given point to a given conic
   section. The given point is called the pole of the line. If
   the given point lies within the curve so that the two
   tangents become imaginary, there is still a real polar line
   which does not meet the curve, but which possesses other
   properties of the polar. Thus the focus and directrix are
   pole and polar. There are also poles and polar curves to
   curves of higher degree than the second, and poles and polar
   planes to surfaces of the second degree.
   [1913 Webster]

WordNet (r) 3.0 (2006):

polar
    adj 1: having a pair of equal and opposite charges
    2: characterized by opposite extremes; completely opposed; "in
       diametric contradiction to his claims"; "diametrical (or
       opposite) points of view"; "opposite meanings"; "extreme and
       indefensible polar positions" [syn: diametric,
       diametrical, opposite, polar]
    3: located at or near or coming from the earth's poles; "polar
       diameter"; "polar zone"; "a polar air mass"; "Antarctica is
       the only polar continent"
    4: of or existing at or near a geographical pole or within the
       Arctic or Antarctic Circles; "polar regions" [ant:
       equatorial]
    5: extremely cold; "an arctic climate"; "a frigid day"; "gelid
       waters of the North Atlantic"; "glacial winds"; "icy hands";
       "polar weather" [syn: arctic, frigid, gelid, glacial,
       icy, polar]
    6: being of crucial importance; "a pivotal event"; "Its pivotal
       location has also exposed it to periodic invasions"- Henry
       Kissinger; "the polar events of this study"; "a polar
       principal" [syn: pivotal, polar]

Moby Thesaurus II by Grady Ward, 1.0:

57 Moby Thesaurus words for "polar":
   Antarctic, Arctic, Siberian, antagonistic, antipodal, antipodean,
   antithetic, antithetical, boundary, brumal, caudal, conclusive,
   confronting, contradictory, contrapositive, contrary, converse,
   counter, definitive, determinative, diamagnetic, diametric,
   electromagnetic, endmost, eventual, extreme, eyeball-to-eyeball,
   facing, farthest, ferromagnetic, final, freezing, frigid, frozen,
   glacial, hibernal, hostile, hyperborean, icy, inverse, last,
   limiting, magnetic, numbing, obverse, opposed, opposing, opposite,
   polaric, polarized, reverse, tail, terminal, terminating,
   terminative, ultimate, wintry