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