Where a bighead can get a new hat (4)
I believe the answer is:
bath
'where a bighead' is the definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.
'can get a new hat' is the wordplay.
'can' becomes 'b' (I can't justify this - if you can you should believe this answer much more).
'get' says to put letters next to each other.
'a new' indicates anagramming the letters.
'hat' is an anagram of 'ath'.
'b'+'ath'='BATH'
Can you help me to learn more?
(Other definitions for bath that I've seen before include "It may be run" , "Water container for washing" , "English spa founded by the Romans" , "Large tub" , "Somerset city with abbey and medicinal waters" .)