The Collaborative International Dictionary of English v.0.48:

Pythagorean \Pyth`a*go"re*an\, a. [L. Pythagoreus, Gr. ?.]
   Of or pertaining to Pythagoras (a Greek philosopher, born
   about 582 b. c.), or his philosophy.
   [1913 Webster]

         The central thought of the Pythagorean philosophy is
         the idea of number, the recognition of the numerical
         and mathematical relations of things.    --Encyc. Brit.
   [1913 Webster]

   Pythagorean proposition (Geom.), the theorem that the
      square described upon the hypothenuse of a plane
      right-angled triangle is equal to the sum of the squares
      described upon the other two sides.

   Pythagorean system (Astron.), the commonly received system
      of astronomy, first taught by Pythagoras, and afterward
      revived by Copernicus, whence it is also called the
      Copernican system.

   Pythagorean letter. See Y.
      [1913 Webster]

WordNet (r) 3.0 (2006):

Copernican system
    n 1: (astronomy) Copernicus' astronomical model in which the
         Earth rotates around the sun