A clownish letter and then some (4)
I believe the answer is:
zany
'a clownish' is the definition.
(thesaurus)
'letter and then some' is the wordplay.
'letter' becomes 'z' (**).
'and then' says to put letters next to each other (I've seen this in other clues).
'some' becomes 'any' ('any' can be similar in meaning to 'some').
'z'+'any'='ZANY'
(Other definitions for zany that I've seen before include "Mad" , "Like a buffoon" , "Comically idiotic" , "Comically eccentric" , "Bizarrely comic" .)