Untrustworthy aunt's a liar and an Aussie, perhaps (10)
I believe the answer is:
australian
'untrustworthy' is the definition.
Although both the answer and definition are adjectives, I don't see how one could define the other.
'aunt's a liar and an aussie perhaps' is the wordplay.
'aunt's a liar' anagrams to 'AUSTRALIAN'.
Though, I am unsure how the anagram is indicated.
Can you help me to learn more?
(Other definitions for australian that I've seen before include "Sydney native" , "Antipodean" , "from Commonwealth" , "Person from down under" , "Native of Perth" .)