Stuffed, some diners ate dinner (5)
I believe the answer is:
sated
'stuffed' is the definition.
(I've seen this before)
'some diners ate dinner' is the wordplay.
'some' says the answer is hidden in the clue (some of the parts of the word are used).
'SATED' is hidden within 'diners ate dinner'.
(Other definitions for sated that I've seen before include "Fed up" , "given more than enough" , "completely filled?" , "Stuffed with food, too full" , "Stuffed, having had a surfeit" .)