Singer making mess of carol, not keeping time (9)
I believe the answer is:
contralto
'singer' is the definition.
(I know that contralto is a type of singer)
'mess of carol not keeping time' is the wordplay.
'mess of' indicates anagramming the letters.
'keeping' indicates putting letters inside (some letters kept inside).
'time' becomes 't' (abbreviation).
'carol'+'not'='carolnot'
'carolnot' anagrammed gives 'contralo'.
'contralo' going around 't' is 'CONTRALTO'.
'making' is the link.
(Other definitions for contralto that I've seen before include "Total corn! (anag)" , "Singer - not car lot (anag)" , "Lowest range for a woman singer" , "Low female voice" , "Lowest female singing voice" .)