Rubaiyat writer (4)
I believe the answer is:
omar
'rubaiyat writer' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for omar that I've seen before include "- Sharif, film actor" , "- - Sharif (films)" , "- Khayyam, Pers. poet" , "Old caliph" , "and 16 Down: Persian poet" .)