Xian vs Xi'an

Xian and Xi'an both are nouns.

Word	Noun	Adjective	Verb	Adverb
Xian	Yes	No	No	No
Xi'an	Yes	No	No	No

As nouns, Xian and Xi'an are synonyms defined as:

Xian and Xi'an: a city of central China; capital of ancient Chinese empire 221-206 BC

Other synonyms of Xian include Changan, Hsian, Sian, Singan.

Xian (noun)	Xi'an (noun)
a city of central China; capital of ancient Chinese empire 221-206 BC	a city of central China; capital of ancient Chinese empire 221-206 BC