Excellent form of beef (5)
I believe the answer is:
bully
This clue might be a double definition.
'excellent' is the first definition.
(I've seen this before)
'form of beef' is the second definition.
'bully' can be an answer for 'beef' (bully beef is corned beef). I'm unsure of the 'form of' bit.
Can you help me to learn more?
(Other definitions for bully that I've seen before include "Very good" , "Tinned beef" , "Intimidating person" , "Well done" , "One persecuting weaker person" .)