Thickhead finally sacked by boss (5)
I believe the answer is:
dumbo
'thickhead' is the definition.
I don't know anything about this answer so I cannot judge whether this works.
'finally sacked by boss' is the wordplay.
'finally' indicates one should take the final letters.
'by' is a charade indicator (letters next to each other).
'boss' becomes 'umbo' (the boss on a shield).
The final letter of 'sacked' is 'd'.
'd'+'umbo'='DUMBO'
Can you help me to learn more?
(Other definitions for dumbo that I've seen before include "1941 Disney film" , "Dope" , "Disney classic of 1941" , "Stupid person" , "1941 film about a young circus elephant born with large ears" .)