Shia vs Shiah

Shia and Shiah both are nouns.

Word	Noun	Adjective	Verb	Adverb
Shia	Yes	No	No	No
Shiah	Yes	No	No	No

As nouns, Shia and Shiah are synonyms defined as:

Shia and Shiah: one of the two main branches of orthodox Islam; mainly in Iran

Other synonyms of Shia include Shiah Islam.

Shia (noun)	Shiah (noun)
one of the two main branches of orthodox Islam; mainly in Iran	one of the two main branches of orthodox Islam; mainly in Iran