John Smith vs Captain John Smith

John Smith and Captain John Smith both are nouns.

Word	Noun	Adjective	Verb	Adverb
John Smith	Yes	No	No	No
Captain John Smith	Yes	No	No	No

As nouns, John Smith and Captain John Smith are synonyms defined as:

John Smith and Captain John Smith: English explorer who helped found the colony at Jamestown, Virginia; was said to have been saved by Pocahontas (1580-1631)

Other synonyms of John Smith include Smith.

John Smith (noun)	Captain John Smith (noun)
English explorer who helped found the colony at Jamestown, Virginia; was said to have been saved by Pocahontas (1580-1631)	English explorer who helped found the colony at Jamestown, Virginia; was said to have been saved by Pocahontas (1580-1631)