The Collaborative International Dictionary of English v.0.48:

Square \Square\ (skw[^a]r), a.
   1. (Geom.) Having four equal sides and four right angles; as,
      a square figure.
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   2. Forming a right angle; as, a square corner.
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   3. Having a shape broad for the height, with rectilineal and
      angular rather than curving outlines; as, a man of a
      square frame.
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   4. Exactly suitable or correspondent; true; just.
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            She's a most triumphant lady, if report be square to
            her.                                  --Shak.
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   5. Rendering equal justice; exact; fair; honest; as, square
      dealing.
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   6. Even; leaving no balance; as, to make or leave the
      accounts square.
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   7. Leaving nothing; hearty; vigorous.
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            By Heaven, square eaters.
            More meat, I say.                     --Beau. & Fl.
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   8. (Naut.) At right angles with the mast or the keel, and
      parallel to the horizon; -- said of the yards of a
      square-rigged vessel when they are so braced.
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   Note: Square is often used in self-explaining compounds or
         combinations, as in square-built, square-cornered,
         square-cut, square-nosed, etc.
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   Square foot, an area equal to that of a square the sides of
      which are twelve inches; 144 square inches.

   Square knot, a knot in which the terminal and standing
      parts are parallel to each other; a reef knot. See Illust.
      under Knot.

   Square measure, the measure of a superficies or surface
      which depends on the length and breadth taken conjointly.
      The units of square measure are squares whose sides are
      the linear measures; as, square inches, square feet,
      square meters, etc.

   Square number. See Square, n., 6.

   Square root of a number or Square root of a quantity
      (Math.), that number or quantity which, multiplied by
      itself, produces the given number or quantity.

   Square sail (Naut.), a four-sided sail extended upon a yard
      suspended by the middle; sometimes, the foresail of a
      schooner set upon a yard; also, a cutter's or sloop's sail
      boomed out. See Illust. of Sail.

   Square stern (Naut.), a stern having a transom and joining
      the counter timbers at an angle, as distinguished from a
      round stern, which has no transom.

   Three-square, Five-square, etc., having three, five,
      etc., equal sides; as, a three-square file.

   To get square with, to get even with; to pay off. [Colloq.]
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WordNet (r) 3.0 (2006):

square sail
    n 1: a four-sided sail set beneath a horizontal yard suspended
         at the middle from a mast