Alienated European, odd, with head of department (9)
I believe the answer is:
estranged
'alienated' is the definition.
(I know that alienated can be written as estranged)
'european odd with head of department' is the wordplay.
'european' becomes 'E' (abbreviation e.g. EU).
'odd' becomes 'strange' (I've seen this before).
'with head of' indicates taking the first letters.
The initial letter of 'department' is 'd'.
'e'+'strange'+'d'='ESTRANGED'
(Other definitions for estranged that I've seen before include "Having become unfriendly or alienated" , "no longer friendly" , "Sad regent (anag) - disaffected" , "A nerd gets (anag) - separated" , "Alienated, disaffected" .)