Jabber possibly anti-American slogan that's empty (8)
I believe the answer is:
ravenous
'empty' is the definition.
(thesaurus)
'jabber possibly anti-american slogan' is the wordplay.
I cannot really see how this works, but
'jabber' could be 'rave' (synonyms) and 'rave' is located in the answer.
'anti' could be 'no' (anti can mean opposing or without) and 'no' is located in the answer.
'american' could be 'us' (abbreviation for United States) and 'us' is present in the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
'that's' acts as a link.
(Other definitions for ravenous that I've seen before include "Wolfish" , "needing to be fed" , "Really hungry, could eat a horse" , "Intensely hungry" , "Voraciously hungry" .)