"Riders to the Sea" playwright (5)
I believe the answer is:
'riders to the sea playwright' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for synge that I've seen before include "John Millington . . . . ., great Irish playwright" , "creator of Playboy character" , "Playboy of the Western World playwright" , "J. M. --, Irish poet/playwright" , "Irish poet and playwright, d. 1909" .)