The Collaborative International Dictionary of English v.0.48:

Shiah \Shi"ah\, prop. n.
   Same as Shiite; when used with a plural verb, the Shiites,
   collectively.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Shiite \Shi"ite\, Shiah \Shi"ah\, n. [Ar. sh[imac]'a[imac]a
   follower of the sect of Ali, fr. sh[imac]'at, sh[imac]'ah, a
   multitude following one another in pursuit of the same
   object, the sect of Ali, fr. sh[=a]'a to follow.]
   A member of that branch of the Mohammedans to which the
   Persians belong. They reject the first three caliphs, and
   consider Ali as being the first and only rightful successor
   of Mohammed. They do not acknowledge the Sunna, or body of
   traditions respecting Mohammed, as any part of the law, and
   on these accounts are treated as heretics by the Sunnites, or
   orthodox Mohammedans.
   [1913 Webster] Shikaree

WordNet (r) 3.0 (2006):

Shiah
    n 1: one of the two main branches of orthodox Islam; mainly in
         Iran [syn: Shiah, Shia, Shiah Islam]