Shape of a London hospital mentioned in speech (5)
I believe the answer is:
guise
'shape' is the definition.
(both can mean a form or appearance)
'a london hospital mentioned in speech' is the wordplay.
'a london hospital' becomes 'Guys' (Guy's Hospital is a London hospital).
'mentioned in speech' shows a homophone (sound like).
'guys' sounds like 'GUISE'.
'of' is the link.
(Other definitions for guise that I've seen before include "Shape; pretence" , "Show" , "General appearance" , "Mask" , "Demeanour" .)