Caster
Part of speech: noun
Definition: A wheeled assembly attached to a larger object at its base to facilitate rolling. A caster usually consists of A shaker with a perforated top for sprinkling condiments such as sugar, salt, pepper, etc.
Castor
Part of speech: noun
Definition: A pivoting roller attached to the bottom of furniture to allow it to be moved.A hat made from the fur of the beaver.A caster; a container with perforated cap for sprinkling (e.g. pepper-castor).