soap tree vs yucca

soap tree and yucca both are nouns.

Word	Noun	Adjective	Verb	Adverb
soap tree	Yes	No	No	No
yucca	Yes	No	No	No

As nouns, yucca is a hypernym of soap tree; that is, yucca is a word with a broader meaning than soap tree:

soap tree: tall arborescent yucca of southwestern United States
yucca: any of several evergreen plants of the genus Yucca having usually tall stout stems and a terminal cluster of white flowers; warmer regions of North America

soap tree (noun)	yucca (noun)
tall arborescent yucca of southwestern United States	any of several evergreen plants of the genus Yucca having usually tall stout stems and a terminal cluster of white flowers; warmer regions of North America