Course served on tray, they say (6)
I believe the answer is:
entree
'course' is the definition.
(course of a meal)
'on tray they say' is the wordplay.
I cannot quite see how this works, but
'on' could be 're' ('on' can be mean 'with reference to') and 're' is present in the answer.
This explanation may well be incorrect...
'served' acts as a link.
Can you help me to learn more?
(Other definitions for entree that I've seen before include "Principal dish and right to enter" , "A dish allowed admittance" , "Starter" , "Privilege of admission, or food dish" , "Dish served between fish and meat courses" .)