Careerist worked a short time in admin department (11)
I believe the answer is:
secretariat
'admin department' is the definition.
(I've seen this before)
'careerist worked a short time' is the wordplay.
'worked' is an anagram indicator.
'short time' becomes 't' (abbreviation for time).
'careerist' is an anagram of 'secretari'.
'secretari'+'a'+'t'='SECRETARIAT'
'in' acts as a link.
(Other definitions for secretariat that I've seen before include "(Adminstrative) office" , "Administrative office" , "administrative department" , "Admin department" , "Office staff" .)