larkspur vs delphinium

larkspur and delphinium both are nouns.

Word	Noun	Adjective	Verb	Adverb
larkspur	Yes	No	No	No
delphinium	Yes	No	No	No

As nouns, delphinium is a hypernym of larkspur; that is, delphinium is a word with a broader meaning than larkspur:

larkspur: any of numerous cultivated plants of the genus Delphinium
delphinium: any plant of the genus Delphinium having palmately divided leaves and showy spikes of variously colored spurred flowers; some contain extremely poisonous substances

larkspur (noun)	delphinium (noun)
any of numerous cultivated plants of the genus Delphinium	any plant of the genus Delphinium having palmately divided leaves and showy spikes of variously colored spurred flowers; some contain extremely poisonous substances