Duke of Wellington vs First Duke of Wellington

Duke of Wellington and First Duke of Wellington both are nouns.

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

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

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

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

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