Senator with endless lie about kin (9)
I believe the answer is:
relations
'kin' is the definition.
(thesaurus)
'senator with endless lie about' is the wordplay.
'with' is a charade indicator (letters next to each other).
'endless' means to remove the last letter.
'about' indicates an anagram.
'lie' with its last letter taken off is 'li'.
'senator'+'li'='senatorli'
'senatorli' anagrammed gives 'RELATIONS'.
(Other definitions for relations that I've seen before include "granny and grandad, perhaps?" , "People connected by blood or marriage" , "kindred?" , "liaison" , "They're connected by blood or marriage" .)