Loud cry “leave quickly” — put energy into it (6)
I believe the answer is:
scream
'loud cry' is the definition.
(I've seen this before)
'leave quickly put energy into it' is the wordplay.
I cannot quite see how this works, but
'energy' could be 'e' (physics symbol as in E=mc2) and 'e' is found in the answer.
'leave' could be 'scram' (to scram is to leave somewhere quickly) and 'scram' is located in the remaining letters.
No letters remain.
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 "Make a piercing sound" , "Howl, shriek" , "Utter a piercing cry" , "funny man" , "A shrill yell as from fright" .)