castor sugar vs powdered sugar

castor sugar and powdered sugar both are nouns.

Word	Noun	Adjective	Verb	Adverb
castor sugar	Yes	No	No	No
powdered sugar	Yes	No	No	No

As nouns, powdered sugar is a hypernym of castor sugar; that is, powdered sugar is a word with a broader meaning than castor sugar:

castor sugar: very finely granulated sugar that was formerly sprinkled from a castor
powdered sugar: sugar granulated into a fine powder

castor sugar (noun)	powdered sugar (noun)
very finely granulated sugar that was formerly sprinkled from a castor	sugar granulated into a fine powder