An ingrate, this rotter? (3)
I believe the answer is:
rat
'this rotter?' is the definition.
('rat' can be a synonym of 'rotter')
'an ingrate' is the wordplay.
'RAT' is hidden within the letters.
However, I am unsure how this is indicated.
Can you help me to learn more?
(Other definitions for rat that I've seen before include "Betrayer" , "Renegade" , "Abandon" , "one who betrayed" , "Despicable person" .)