Yell "Be off!" grabbing the key (6)
I believe the answer is:
scream
'yell' is the definition.
(I know that scream is a type of yell)
'be off grabbing the key' is the wordplay.
I cannot quite see how this works, but
'be' could be 'am' and 'am' is present in the answer.
'key' could be 'e' (musical key) and 'e' 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 scream that I've seen before include "Loud piercing cry" , "Funny person; cry" , "irresistibly funny person" , "A shrill yell as from fright" , "Hoot - yell in pain" .)