A beefy uppercut (7)
I believe the answer is:
sirloin
'a beefy uppercut' is the definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.
This is the entire clue.
Can you help me to learn more?
(Other definitions for sirloin that I've seen before include "Good cut of beef" , "Joint of beef" , "Upper part of loin of beef" , "Quality cut of beef loin" , "Choice cut of beef" .)