A muffineer is essentially a salt shaker; it's a small container with a perforated top which is used to shake out powders like sugar, salt, and talc in a controlled way.  You may also hear a muffineer referred to as a caster or castor, depending on regional dialect, and of course it is perfectly acceptable to call a muffineer a shaker, since that's what it is.

During the Victorian era shakers were used to sprinkle sugar or cinnamon and sugar on bread of muffins.  This muffineer is 4 3/4” high.