caster sugar
noun🔊/ˈkɑːstə ʃʊɡə(r)/
🔊/ˈkæstər ʃʊɡər/
(also castor sugar)
[uncountable] (British English)white sugar in the form of very fine grains, used in cooking 幼砂糖 Word Originmid 19th cent.: so named because it was suitable for use in a castor, a small container with holes in the top, used for sprinkling sugar.