castor sugar vs caster sugar

castor sugar and caster sugar both are nouns.

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

As nouns, castor sugar and caster sugar are synonyms defined as:

castor sugar and caster sugar: very finely granulated sugar that was formerly sprinkled from a castor

castor sugar (noun)	caster sugar (noun)
very finely granulated sugar that was formerly sprinkled from a castor	very finely granulated sugar that was formerly sprinkled from a castor