That is Victor in pain, head of department realised (8)
I believe the answer is:
achieved
'realised' is the definition.
(thesaurus)
'that is victor in pain head of department' is the wordplay.
'that is' becomes 'ie' ('i.e.' can be a synonym of 'that is').
'victor' becomes 'v' (phonetic alphabet: alpha, bravo, charlie etc.).
'in' means one lot of letters goes inside another.
'pain' becomes 'ache' (ache is a kind of pain**).
'head of' says to take the initial letters.
The first letter of 'department' is 'd'.
'ie'+'v'='iev'
'iev' placed into 'ache' is 'achieve'.
'achieve'+'d'='ACHIEVED'
(Other definitions for achieved that I've seen before include "obtained" , "Attained, got there" , "Attained, reached objective" , "Gained with effort" , "Reached or accomplished" .)