Definition of cyathus:
(n) :
A ladle, especially (historical) a small one used for serving wine in ancient Greece and Rome.
(n) :
(historical) An ancient Roman unit of liquid measure reckoned as the volume of 1⅔ Roman ounce of wine and equivalent to about 45 mL although differing slightly over time.
(n) :
(historical) Synonym of kyathos (“an ancient ladle and serving beaker”).