The female uses the same key (3)
I believe the answer is:
doe
'the female' is the definition.
(female deer)
'the same key' is the wordplay.
'the same' becomes 'do' (abbreviation for ditto).
'key' becomes 'e' (musical key).
'do'+'e'='DOE'
'uses' acts as a link.
(Other definitions for doe that I've seen before include "Mummy rabbit" , "A female deet" , "Rabbit, perhaps" , "partner for a buck" , "possible mate for Rudolph?" .)