Opening hospital department after five (4)
I believe the answer is:
vent
'opening' is the definition.
(vent is a kind of opening)
'hospital department after five' is the wordplay.
'hospital department' becomes 'ent'.
'after' means one lot of letters go next to another.
'five' becomes 'v' (roman numeral).
'ent' after 'v' is 'VENT'.
(Other definitions for vent that I've seen before include "Opening of a volcano" , "Aperture to allow an escape" , "Opening for air/gas" , "Outlet; slit in jacket" , "Broadcast" .)