Dish encountered in hospital department, on Sundays principally (9)
I believe the answer is:
entremets
'dish' is the definition.
(I've seen this before)
'encountered in hospital department on sundays principally' is the wordplay.
'encountered' becomes 'met' ('meet' can be a synonym of 'encounter').
'in' means one lot of letters goes inside another.
'hospital department' becomes 'ent'.
'on' says to put letters next to each other.
'sundays principally' becomes 'res' (I am not sure about this - if you are sure you should believe this answer much more).
'ent'+'res'='entres'
'met' put into 'entres' is 'ENTREMETS'.
Can you help me to learn more?
(Other definitions for entremets that I've seen before include "French course" , "Dish" .)