Ivan is bent on intrusion (8)
I believe the answer is:
invasion
'intrusion' is the definition.
('invasion' can be a synonym of 'intrusion')
'ivan is bent on' is the wordplay.
'bent' indicates an anagram.
'ivan'+'is'='ivanis'
'ivanis' is an anagram of 'invasi'.
'invasi'+'on'='INVASION'
(Other definitions for invasion that I've seen before include "Offensive" , "Unwelcome encroachment on another country" , "Encroachment, intrusion" , "Encroachment by enemy" , "Unwelcome intrusion" .)