Decline record by mail order (8)
I believe the answer is:
disclaim
'decline' is the definition.
(thesaurus)
'record by mail order' is the wordplay.
'record' becomes 'disc' ('disc' can be a synonym of 'record'**).
'by' says to put letters next to each other.
'order' indicates an anagram.
'mail' with letters rearranged gives 'laim'.
'disc'+'laim'='DISCLAIM'
(Other definitions for disclaim that I've seen before include "Deny, refuse to acknowledge" , "Deny or relinquish" , "Forswear" , "Renounce" , "Disown or deny, maybe responsibility" .)