Commanding Officer carried over a drink (5)
I believe the answer is:
cocoa
'drink' is the definition.
(cocoa is a kind of drink)
'commanding officer carried over a' is the wordplay.
'commanding officer' becomes 'co'.
'carried' says to put letters next to each other.
'over' becomes 'co' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'co'+'co'+'a'='COCOA'
Can you help me to learn more?
(Other definitions for cocoa that I've seen before include "Bedtime drink made from powder" , "Kind of chocolate drink" , "Medium to dark brown" , "Hot bedtime drink" , "Reddish brown" .)