Prince Charlie with that old-fashioned calm (7)
I believe the answer is:
halcyon
'calm' is the definition.
(I've seen this in another clue)
'prince charlie with that old-fashioned' is the wordplay.
'prince' becomes 'hal' (Shakespearean nickname of Henry V when a prince).
'charlie' becomes 'C' (phonetic alphabet: alpha, bravo, charlie etc.).
'with' says to put letters next to each other.
'that old-fashioned' becomes 'yon' ('yon' is an archaic word for 'that').
'hal'+'c'+'yon'='HALCYON'
(Other definitions for halcyon that I've seen before include "Bird" , "Of a period, happy and peaceful - say youth" , "Balmy" , "Tropical kingfisher" , "Such days are calm and happy" .)