Noel's upset about a bighead being posh (5)
I believe the answer is:
noble
'posh' is the definition.
(thesaurus)
'noel's upset about a bighead' is the wordplay.
'upset' indicates an anagram.
'about' indicates putting letters inside.
'a bighead' becomes 'b' (the head letter of 'big').
'noel' is an anagram of 'nole'.
'nole' placed around 'b' is 'NOBLE'.
'being' acts as a link.
(Other definitions for noble that I've seen before include "Eminent" , "Stately" , "Illustrious, peer" , "aristocrat, maybe" , "Illustrious - of high birth - old gold coin" .)