Support only half the letters? (4)
I believe the answer is:
abet
'support' is the definition.
(thesaurus)
'only half the letters?' is the wordplay.
'only half' means to take half the letters.
'the letters?' becomes 'alphabet' (I've seen this before).
'alphabet' cut in half is 'ABET'.
(Other definitions for abet that I've seen before include "Assist (a criminal)" , "Criminally endorse" , "Give aid to" , "support wrongdoing" , "Assist illegally" .)