Fool's easy to name (9)
I believe the answer is:
simpleton
'fool's' is the definition.
(thesaurus)
'easy to name' is the wordplay.
'easy' becomes 'simple' ('simple' can be similar in meaning to 'easy').
'name' becomes 'n' (common abbreviation e.g. on forms).
'simple'+'to'+'n'='SIMPLETON'
(Other definitions for simpleton that I've seen before include "Unintelligent person" , "Simon for one" , "Dunce" , "Gullible type" , "Ninny" .)