Aptly, Evan withholds the odd request (4)
I believe the answer is:
plea
'request' is the definition.
(I know that plea is a type of appeal)
'aptly evan withholds the odd' is the wordplay.
'withholds the odd' means one should take alternating letters (letters in odd-numbered positions removed).
'aptly'+'evan'='aptlyevan'
The alternate letters of 'aptlyevan' are 'PLEA'.
(Other definitions for plea that I've seen before include "Excuse, entreaty" , "Negotiation between prosecutor and defendant" , "Request for mercy?" , "Earnest appeal" , "Answer made by the accused to the charge" .)