Band of commandos at hospital (4)
I believe the answer is:
sash
'band' is the definition.
(sash is a kind of band)
'commandos at hospital' is the wordplay.
'commandos' becomes 'sas' (Special Air Service).
'at' means one lot of letters go next to another.
'hospital' becomes 'h'.
'sas'+'h'='SASH'
'of' acts as a link.
(Other definitions for sash that I've seen before include "Window frame; cloth strip (worn over shoulder)" , "Style of window" , "Piece of cloth round waist or shoulder" , "Decorative band" , "Long strip of material - window frame" .)