Egyptian goddess whose headdress in some depictions is a sun disc between cow horns (4)
![Ross](/clue/static/ross-mug.min.png)
I believe the answer is:
isis
(Other definitions for isis that I've seen before include "Sister of Osiris" , "Egyptian goddess and jihadist group" , "Repetitive Egyptian goddess" , "where one might take a punt" , "Wife of Osiris" .)