Bighead has different trouble (6)
I believe the answer is:
bother
'trouble' is the definition.
(I know that trouble can be written as bother)
'bighead has different' is the wordplay.
'bighead' becomes 'b' (head letter of 'big').
'has' says to put letters next to each other.
'different' becomes 'other' (similar in meaning).
'b'+'other'='BOTHER'
(Other definitions for bother that I've seen before include "Fuss, ado" , "Discommode, annoy" , "Pester, aggravate" , "Badger" , "Fuss; oh no!" .)