TV, one of many used by painter (4)
I believe the answer is:
tube
'tv' is the definition.
(I've seen this before)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for tube that I've seen before include "Hollow cylindrical object" , "Transport system" , "channel" , "Underground transport" , "London Underground or long cylinder" .)