Tenor with power covering Queen. Idiot ... (5)
I believe the answer is:
twerp
'idiot' is the definition.
(I've seen this before)
'tenor with power covering queen' is the wordplay.
'tenor' becomes 't'.
'with' becomes 'w' (abbreviation**).
'power' becomes 'p'.
'covering' is an insertion indicator.
'queen' becomes 'er' (abbreviation for Elizabeth Regina).
'w'+'p'='wp'
'wp' placed around 'er' is 'werp'.
't'+'werp'='TWERP'
(Other definitions for twerp that I've seen before include "Foolish fellow" , "Silly-billy" , "Nitwit" , "Foolish person (slang)" , "dope" .)