Handing over additional information about a carol (7)
I believe the answer is:
passing
'handing' is the definition.
('pass' can be a synonym of 'hand')
'over additional information about a carol' is the wordplay.
'over' says to put letters next to each other.
'additional information' becomes 'PS' (postscript written at the end of a letter).
'about' means one lot of letters goes inside another.
'carol' becomes 'sing' (I've seen this before).
'ps' going around 'a' is 'pas'.
'pas' next to 'sing' is 'PASSING'.
(Other definitions for passing that I've seen before include "Ephemeral" , "Casual - death" , "Short-lived - death" , "Overtaking" .)