Mug taken in by compassion and honesty (7)
I believe the answer is:
probity
'honesty' is the definition.
(probity is a kind of honesty)
'mug taken in by compassion' is the wordplay.
'mug' becomes 'rob' (I've seen this in other clues).
'taken in by' means one lot of letters goes inside another.
'compassion' becomes 'pity' (pity is a kind of compassion).
'rob' placed within 'pity' is 'PROBITY'.
'and' acts as a link.
(Other definitions for probity that I've seen before include "integrity's demanded" , "uprightness" , "Honesty, decency" , "Integrity" .)