Really healthy Republican friend (9)
I believe the answer is:
literally
'really' is the definition.
(thesaurus)
'healthy republican friend' is the wordplay.
'healthy' becomes 'lite' (as in a lite version of a drink or food).
'republican' becomes 'r' (abbreviation).
'friend' becomes 'ally' (I've seen this before).
'lite'+'r'+'ally'='LITERALLY'
(Other definitions for literally that I've seen before include "Without exaggeration" , "Absolutely" , "According to the letter, exactly" , "Actually, really" , "Verbatim" .)