Vacuous Carry On Henry's opening is carefree (7)
I believe the answer is:
halcyon
'carefree' is the definition.
(I've seen this before)
'vacuous carry on henry's opening' is the wordplay.
'vacuous' means to remove the middle letters.
'henry' becomes 'hal' (short for Henry).
'opening' says to put letters next to each other (some letters appear before or \'open\' others).
'carry' with its centre removed is 'cy'.
'cy'+'on'='cyon'
'cyon' put after 'hal' is 'HALCYON'.
'is' acts as a link.
(Other definitions for halcyon that I've seen before include "Kingfisher genus" , "Such days are calm and happy" , "Any loch? (anag)" , "Of a period, happy and peaceful - say youth" , "Calm and happy - kingfisher" .)