WordNet (r) 3.0 (2006):

graduate school
    n 1: a school in a university offering study leading to degrees
         beyond the bachelor's degree [syn: graduate school, grad
         school]

Moby Thesaurus II by Grady Ward, 1.0:

24 Moby Thesaurus words for "graduate school":
   academe, academia, alma mater, college, college of engineering,
   community college, degree-granting institution, four-year college,
   institute of technology, ivied halls, journalism school,
   junior college, law school, medical school, multiversity, normal,
   normal school, postgraduate school, school of communications,
   school of education, two-year college, university,
   university college, varsity