leopardbane vs leopard's-bane

leopardbane and leopard's-bane both are nouns.

Word	Noun	Adjective	Verb	Adverb
leopardbane	Yes	No	No	No
leopard's-bane	Yes	No	No	No

As nouns, leopardbane and leopard's-bane are synonyms defined as:

leopardbane and leopard's-bane: any of several herbs of the genus Doronicum having alternate often clasping stem leaves cultivated for their long stalks of yellow flower heads

leopardbane (noun)	leopard's-bane (noun)
any of several herbs of the genus Doronicum having alternate often clasping stem leaves cultivated for their long stalks of yellow flower heads	any of several herbs of the genus Doronicum having alternate often clasping stem leaves cultivated for their long stalks of yellow flower heads