The Collaborative International Dictionary of English v.0.48:

Foursquare \Four"square`\ (f[=o]r"skw[^a]r`), a.
   Having four sides and four equal angles. --Sir W. Raleigh.
   [1913 Webster]

WordNet (r) 3.0 (2006):

foursquare
    adv 1: in a square position; "the building stood foursquare"
    2: with firmness and conviction; without compromise; "he stood
       foursquare for religious liberty and toleration"- C.G.Bowers;
       "dealt straightforwardly with all issues" [syn: squarely,
       foursquare, straightforwardly]
    adj 1: characterized by firm and unwavering conviction; "a
           foursquare refusal to yield"
    n 1: (geometry) a plane rectangle with four equal sides and four
         right angles; a four-sided regular polygon; "you can
         compute the area of a square if you know the length of its
         sides" [syn: square, foursquare]

Moby Thesaurus II by Grady Ward, 1.0:

53 Moby Thesaurus words for "foursquare":
   aboveboard, authentic, biquadratic, bona fide, cube-shaped, cubed,
   cubic, cubiform, cuboid, diced, fair and square, four, four-legged,
   four-rayed, genuine, good-faith, oblong, on the level,
   on the square, on the up-and-up, open, open and aboveboard,
   orthogonal, quadrangular, quadrate, quadratic, quadric, quadriform,
   quadrilateral, quadrinomial, quadrivalent, quadruped, quartic,
   quartile, quaternary, rectangular, rhombic, rhomboid,
   single-hearted, square, square-dealing, square-shooting, straight,
   straight-shooting, tetractinal, tetrad, tetragonal, tetrahedral,
   tetravalent, trapezohedral, trapezoid, up-and-up, veritable