Wordnet 3.0
NOUN (1)
1. 
 a state of mind that is discussed as if it were a place; 
- Example: "he lived in the ivory tower of speculation"- Example: "they viewed universities as ivory towers"
WordNet (r) 3.0 (2006):
ivory tower
    n 1: a state of mind that is discussed as if it were a place;
         "he lived in the ivory tower of speculation"; "they viewed
         universities as ivory towers"
Moby Thesaurus II by Grady Ward, 1.0:
18 Moby Thesaurus words for "ivory tower":
   adytum, ashram, cell, cloister, den, hermitage, hideaway, hideout,
   hiding place, holy of holies, lair, mew, privacy, recess, retreat,
   sanctum, sanctum sanctorum, secret place