pink of my John vs viola

pink of my John and viola both are nouns.

Word	Noun	Adjective	Verb	Adverb
pink of my John	Yes	No	No	No
viola	Yes	No	No	No

As nouns, viola is a hypernym of pink of my John; that is, viola is a word with a broader meaning than pink of my John:

pink of my John: a common and long cultivated European herb from which most common garden pansies are derived
viola: any of the numerous plants of the genus Viola

pink of my John (noun)	viola (noun)
a common and long cultivated European herb from which most common garden pansies are derived	any of the numerous plants of the genus Viola
	a bowed stringed instrument slightly larger than a violin, tuned a fifth lower