| Noun | 1. | castor sugar - very finely granulated sugar that was formerly sprinkled from a castor powdered sugar - sugar granulated into a fine powder Britain, Great Britain, U.K., UK, United Kingdom, United Kingdom of Great Britain and Northern Ireland - a monarchy in northwestern Europe occupying most of the British Isles; divided into England and Scotland and Wales and Northern Ireland; `Great Britain' is often used loosely to refer to the United Kingdom |