urban center vs Sian

urban center and Sian both are nouns.

Word	Noun	Adjective	Verb	Adverb
urban center	Yes	No	No	No
Sian	Yes	No	No	No

urban center (noun)	Sian (noun)
a large and densely populated urban area; may include several independent administrative districts	a city of central China; capital of ancient Chinese empire 221-206 BC