Criminal lot rat out one who's known to sing (9)
I believe the answer is:
contralto
'one who's known to sing' is the definition.
I can't judge whether this definition defines the answer.
'criminal lot rat out' is the wordplay.
'criminal' becomes 'con' (abbreviation for 'convict').
'out' indicates anagramming the letters (out can mean wrong or inaccurate).
'lot'+'rat'='lotrat'
'lotrat' with letters rearranged gives 'tralto'.
'con'+'tralto'='CONTRALTO'
Can you help me to learn more?
(Other definitions for contralto that I've seen before include "Female voice of the lower register." , "Lowest female singer" , "Singer - not car lot (anag)" , "Lowest range for a woman singer" , "Total corn! (anag)" .)