WordNet (r) 3.0 (2006):

secondary school
    n 1: a school for students intermediate between elementary
         school and college; usually grades 9 to 12 [syn: secondary
         school, lyceum, lycee, Gymnasium, middle school]

Moby Thesaurus II by Grady Ward, 1.0:

18 Moby Thesaurus words for "secondary school":
   Gymnasium, Latin school, Realgymnasium, Realschule, academy,
   grammar school, high, high school, intermediate school,
   junior high, junior high school, middle school, prep school,
   preparatory school, public school, seminary, senior high,
   senior high school