Clever bighead, never wrong (6)
I believe the answer is:
bright
'clever' is the definition.
(I've seen this before)
'bighead never wrong' is the wordplay.
I cannot really see how this works, but
'bighead' could be 'b' (the head letter of 'big') and 'b' is found in the answer.
The remaining letters 'right' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for bright that I've seen before include "Intelligent, lively" , "supporter of free trade" , "Clever; fine" , "Dazzling or intelligent" , "Shiny" .)