Remaining boy carries round excessive burden (8)
I believe the answer is:
overload
'excessive burden' is the definition.
'overload' can be an answer for 'burden' (overload is a kind of burden). I am not sure about the 'excessive' bit.
'remaining boy carries round' is the wordplay.
'remaining' becomes 'over' (as in 'we ate them all but had one over').
'boy' becomes 'lad' (informal term for boy).
'carries' means one lot of letters goes inside another (inserted letters carried inside).
'round' becomes 'o' (round can mean a round object).
'lad' enclosing 'o' is 'load'.
'over'+'load'='OVERLOAD'
Can you help me to learn more?
(Other definitions for overload that I've seen before include "Excessive amount" , "Burden excessively" , "Excessive electrical demand" , "saddle" , "Excessive demand (on a system)" .)