Charlie's got the hump - the fathead! (5)
I believe the answer is:
chump
'the fathead' is the definition.
(thesaurus)
'charlie's got the hump' is the wordplay.
'charlie' becomes 'C' (phonetic alphabet).
'got' says to put letters next to each other.
'c'+'hump'='CHUMP'
(Other definitions for chump that I've seen before
include
"Fool - sort of chop"
,
"Dolt"
,
"Foolish person"
,
"Blockhead"
,
"Thick