Wellington vs Duke of Wellington

Wellington and Duke of Wellington both are nouns.

Word	Noun	Adjective	Verb	Adverb
Wellington	Yes	No	No	No
Duke of Wellington	Yes	No	No	No

As nouns, Wellington and Duke of Wellington are synonyms defined as:

Wellington and Duke of Wellington: British general and statesman; he defeated Napoleon at Waterloo; subsequently served as Prime Minister (1769-1852)

Other synonyms of Wellington include Arthur Wellesley, First Duke of Wellington, Iron Duke.

Wellington (noun)	Duke of Wellington (noun)
(19th century) a man's high tasseled boot	British general and statesman; he defeated Napoleon at Waterloo; subsequently served as Prime Minister (1769-1852)
the capital of New Zealand
British general and statesman; he defeated Napoleon at Waterloo; subsequently served as Prime Minister (1769-1852)