soap tree vs soap-weed

soap tree and soap-weed both are nouns.

Word	Noun	Adjective	Verb	Adverb
soap tree	Yes	No	No	No
soap-weed	Yes	No	No	No

As nouns, soap tree and soap-weed are synonyms defined as:

soap tree and soap-weed: tall arborescent yucca of southwestern United States

Other synonyms of soap tree include soapweed, Yucca elata.

soap tree (noun)	soap-weed (noun)
tall arborescent yucca of southwestern United States	tall arborescent yucca of southwestern United States