Leaves office, concerned with omens? (7)
I believe the answer is:
resigns
'leaves office' is the definition.
(as in resigning from political office)
'concerned with omens?' is the wordplay.
'concerned with' becomes 're' (re can mean regarding, concerning).
'omens?' becomes 'signs' (omen is a kind of sign).
're'+'signs'='RESIGNS'
(Other definitions for resigns that I've seen before include "does the honourable thing" , "Gives up (a post)" , "abdicates" , "Leaves job voluntarily" .)