The Collaborative International Dictionary of English v.0.48:

Uraeus \U*rae"us\, n. [NL., fr. L. uraeus pertaining to a tail,
   Gr. ?, fr. ? tail.] (Egypt. Archaeol.)
   A serpent, or serpent's head and neck, represented on the
   front of the headdresses of divinities and sovereigns as an
   emblem of supreme power.
   [Webster 1913 Suppl.]