Repeat song endlessly: nothing can end it (5)
I believe the answer is:
ditto
'repeat' is the definition.
(I know that ditto is a more specific form of the action repeat)
'song endlessly nothing can end it' is the wordplay.
I cannot quite understand how this works, but
'nothing' could be 'o' (O resembles 0) and 'o' is found within the answer.
'it' could be 't' (abbreviation. e.g. in 'tis) and 't' is found in the answer.
The remaining letters 'dit' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for ditto that I've seen before include "couple of marks" , "Repeat (instruction)" , "Repeat the word above" , "In lists, the same again with two small marks" , "Copy" .)