Sing creditably with nothing on? (5)
I believe the answer is:
croon
'sing' is the definition.
(I know that croon is a more specific form of the action sing)
'creditably with nothing on?' is the wordplay.
'creditably' becomes 'cr' (I can't justify this - if you can you should give a lot more credence to this answer).
'with' says to put letters next to each other.
'nothing' becomes 'O' (looks like zero - 0).
'cr'+'o'+'on'='CROON'
Can you help me to learn more?
(Other definitions for croon that I've seen before include "Sing with a soft voice" , "Sing softly" , "Sing like Bing" , "Sing in a soft low tone" .)