Idiot singer missing introduction (3)
I believe the answer is:
ass
'idiot' is the definition.
(both can mean a stupid person)
'singer missing introduction' is the wordplay.
'singer' becomes 'bass' (bass is a kind of singer).
'missing introduction' means to remove the first letter.
'bass' with its initial letter taken away is 'ASS'.
(Other definitions for ass that I've seen before include "Dolt" , "twit!" , "Bottom, temporarily" , "Trump's behind" , "Democratic mascot" .)