Animal's pong accepted by one elderly relative (7)
I believe the answer is:
inhuman
'animal's' is the definition.
(thesaurus)
'pong accepted by one elderly relative' is the wordplay.
'pong' becomes 'hum' (I've seen this before).
'accepted by' indicates putting letters inside.
'one' becomes 'i' (Roman numeral).
'elderly relative' becomes 'nan' (I've seen this before).
'i'+'nan'='inan'
'hum' placed inside 'inan' is 'INHUMAN'.
(Other definitions for inhuman that I've seen before include "Pitiless - barbarous" , "Cruel, barbaric" , "Cruel, bestial" , "Unfeelingly cruel" , "Nasty" .)