washing powder vs built-soap powder

washing powder and built-soap powder both are nouns.

Word	Noun	Adjective	Verb	Adverb
washing powder	Yes	No	No	No
built-soap powder	Yes	No	No	No

As nouns, washing powder and built-soap powder are synonyms defined as:

washing powder and built-soap powder: soap in powdered form mixed with alkaline builders

Other synonyms of washing powder include soap powder.

washing powder (noun)	built-soap powder (noun)
soap in powdered form mixed with alkaline builders	soap in powdered form mixed with alkaline builders