WordNet (r) 3.0 (2006):

Sion
    n 1: originally a stronghold captured by David (the 2nd king of
         the Israelites); above it was built a temple and later the
         name extended to the whole hill; finally it became a
         synonym for the city of Jerusalem; "the inhabitants of
         Jerusalem are personified as `the daughter of Zion'" [syn:
         Zion, Sion]
    2: Jewish republic in southwestern Asia at eastern end of
       Mediterranean; formerly part of Palestine [syn: Israel,
       State of Israel, Yisrael, Zion, Sion]
    3: an imaginary place considered to be perfect or ideal [syn:
       Utopia, Zion, Sion]

Easton's 1897 Bible Dictionary:

Sion
   elevated. (1.) Denotes Mount Hermon in Deut. 4:48; called Sirion
   by the Sidonians, and by the Amorites Shenir (Deut. 3:9). (See HERMON.)

     (2.) The Greek form of Zion (q.v.) in Matt. 21:5; John 12:15.


Hitchcock's Bible Names Dictionary (late 1800's):

Sion, noise; tumult