soap powder vs washing powder

soap powder and washing powder both are nouns.

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

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

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

Other synonyms of soap powder include built-soap powder.

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