John: name for Scots lad (4)
I believe the answer is:
loon
'scots lad' is the definition.
(Scottish term for a boy)
'john name' is the wordplay.
'john' becomes 'loo' (both can mean a toilet).
'name' becomes 'n' (common abbreviation e.g. on forms).
'loo'+'n'='LOON'
'for' is the link.
(Other definitions for loon that I've seen before include "Fool" , "Diving bird with wild cry - sounds crazy" , "Diver; silly person" , "Fish-eating diving bird" , "Noddy" .)