One who is switched on? (4,4)
I believe the answer is:
live wire
'one who is switched on?' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'one who is switched on?' is the wordplay.
I cannot quite understand how this works, but
'one' could be 'i' (Roman numeral) and 'i' is located in the answer.
'on?' could be 're' (regarding) and 're' is present in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for live wire that I've seen before include "Brown covering for this" , "isn't it shocking?" , "'One is very energetic, almost electric (4,4)'" , "Life and soul of party" , "Conductor charged with electricity - energetic person" .)