Part sung in key, another key briefly eclipsing it (9)
I believe the answer is:
contralto
'part' is the definition.
(thesaurus)
'sung in key another key briefly eclipsing it' is the wordplay.
I cannot really understand how this works, but
'key' could be 'alt' (the Alt keyboard button) and 'alt' is found in the answer.
'another' could be 'r' (I've seen this in other clues) and 'r' is located in the answer.
'it' could be 't' (abbreviation. e.g. in 'tis) and 't' is found within the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for contralto that I've seen before include "Female voice of the lower register." , "deep, for women" , "Total corn! (anag)" , "Singer - not car lot (anag)" , "Lowest female singer" .)