This chap needs son for everything (5)
I believe the answer is:
cosmo
'this chap needs son for everything' is the definition.
'Cosmo' can be an answer for 'chap'. I'm not certain of the remainder of the definition.
'this chap needs son' is the wordplay.
'this chap' becomes 'Cos'.
'needs son' becomes 'mo' (I can't justify this - if you can you should believe this answer much more).
'cos'+'mo'='COSMO'
Can you help me to learn more?
(Other definitions for cosmo that I've seen before include "Fellow" , "- Lang, Archbishop of Canterbury nineteen twenty eight to nineteen forty two" , "One of Florence's Medici rulers" .)