Polish hospital observed nurses (5)
I believe the answer is:
sheen
'polish' is the definition.
(I've seen this before)
'hospital observed nurses' is the wordplay.
'hospital' becomes 'h'.
'observed' becomes 'seen' (synonyms).
'nurses' means one lot of letters goes inside another (nurse can mean to hold onto or harbour).
'h' put into 'seen' is 'SHEEN'.
(Other definitions for sheen that I've seen before include "to the west of Putney" , "Surface shine" , "Patina" , "Superficial brightness" , "Radiance" .)