Lordly bighead Noel's upset about (5)
I believe the answer is:
noble
'lordly' is the definition.
(similar in meaning)
'bighead noel's upset about' is the wordplay.
'bighead' becomes 'b' (the head letter of 'big').
'upset' indicates anagramming the letters.
'about' means one lot of letters goes inside another.
'noel' anagrammed gives 'nole'.
'b' going into 'nole' is 'NOBLE'.
(Other definitions for noble that I've seen before include "Having high moral qualities" , "Having high moral character" , "Impressive in appearance" , "Dignified" , "titled person" .)