Arm of a starfish (3)
I believe the answer is:
ray
'arm of a starfish' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for ray that I've seen before include "Sunbeam or flat fish" , "Shaft, beam" , "A little light" , "Beam; man's name" , "Narrow beam of light" .)