An appeal, or maybe part of one (4)
I believe the answer is:
plea
'an appeal' is the definition.
(I know that plea is a type of appeal)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for plea that I've seen before include "Petition or supplication" , "Intercession" , "(and 14) Enjoyment - gratification" , "Answer made by the accused to the charge" , "Earnest request, prayer" .)