Is it ensure, insure, or assure?
1540s, from Latin Pythagoreus "of or pertaining to Pythagoras," Greek philosopher of Samos (6c. B.C.E.), whose teachings included transmigration of the soul and vegetarianism (these are some of the commonest early allusions in English). The Pythagorean theorem is the 47th of the first book of Euclid.