I'm overwhelmed by a friend's ill-will (8)
I believe the answer is:
acrimony
'ill-will' is the definition.
(thesaurus)
'i'm overwhelmed by a friend's' is the wordplay.
'overwhelmed by' indicates putting letters inside (I've seen this in other clues).
'friend' becomes 'crony' (crony is a kind of friend).
'a'+'crony'='acrony'
'im' inserted within 'acrony' is 'ACRIMONY'.
(Other definitions for acrimony that I've seen before include "Bitterness of manner or words" , "Bitter feeling" , "Bitterness or ill-feeling" , "Acronym I made out of bitterness" , "Asperity" .)